UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(RULE 14a-101)

Information Required in Proxy Statement

Schedule 14A Information

Proxy Statement Pursuant to Section 14(a) of the Securities

Securities Exchange Act of 1934 (Amendment No.                 )

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

Check the appropriate box:

ApolloMidcap Financial Investment Corporation

(Name of Registrant as Specified inIn Its Charter)

(Name of Person(s) Filing Proxy Statement if other than the Registrant)

Payment of Filing Fee (Check the appropriate box)all boxes that apply):

☐	Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11

9 West 57th Street

New York, New York 10019

June 16, 2020May 1, 2023

Dear Stockholder:

You are cordially invited to attend the 20202023 Annual Meeting of Stockholders of ApolloMidCap Financial Investment Corporation, a Maryland corporation (the “Company”), to be held virtually on August 11, 2020July 10, 2023 at 10:00 a.m., Eastern Daylight Time at www.virtualshareholdermeeting.com/AINV2020.MFIC2023.

The Notice of Virtual Annual Meeting of Stockholders accompanying this letter provides an outline of the business to be conducted at the meeting. At the meeting, you will be asked: (1) to consider and vote upon the election of threetwo Class I directors;Directors; (2) to consider and vote upon the ratification of the selection of PricewaterhouseCoopersDeloitte & Touche LLP (“Deloitte”) as the Company’s independent registered public accounting firm for the fiscal year ending MarchDecember 31, 2021;2023; and (3) to transact such other business as may properly come before the meeting and any postponements or adjournments thereof. I will also report on the progress of the Company during the past year and respond to stockholders’ questions.

You have the right to receive notice of and to vote at the Annual Meeting of Stockholders if you were a stockholder of record at the close of business on June 12, 2020.April 24, 2023. It is important that your shares be represented at the Annual Meeting. Please follow the instructions on the Notice of Internet Availability of Proxy Materials and authorize a proxy via the Internet or telephone to vote your shares. I encourage you to vote via the Internet as it saves us significant time and processing costs. However, the Notice of Internet Availability of Proxy Materials includes instructions on how to request a hard copy of the proxy statement and proxy card for the Annual Meeting free of charge, and you may vote your proxy by returning your proxy card to us after you request the hard copy materials. Your vote and participation in the governance of the Company is very important to us.

Sincerely yours,

Sincerely yours,

John J. Hannan

Chairman of the Board of Directors

Howard Widra

Executive Chairman of the Board of Directors

APOLLOMIDCAP FINANCIAL INVESTMENT CORPORATION

9 West 57th Street

New York, New York 10019

(212)515-3450

NOTICE OF VIRTUAL ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON AUGUST 11, 2020JULY 10, 2023

Online Meeting Only – No Physical Meeting Location

To the Stockholders of ApolloMidCap Financial Investment Corporation:

The 20202023 Annual Meeting of Stockholders (the “Meeting”) of ApolloMidCap Financial Investment Corporation, a Maryland corporation (the “Company”), will be held virtually on Thursday, August 11, 2020Monday, July 10, 2023 at 10:00 a.m., Eastern Daylight Time, at www.virtualshareholdermeeting.com/AINV2020,MFIC2023, for the following purposes:

The 20202023 Annual Meeting of Stockholders of the Company will only be accessible virtually via live webcast over the Internet at www.virtualshareholdermeeting.com/AINV2020.MFIC2023.

You have the right to receive notice of and to vote at the meeting if you were a stockholder of record at the close of business on June 12, 2020.April 24, 2023. A list of these stockholders will be open for examination by any stockholder for any purpose germane to the Annual Meeting for a period of 10 days prior to the Annual Meeting at the Company’s principal executive offices at 9 West 57th Street, New York, New York 10019, and electronically during the Annual Meeting at www.virtualshareholdermeeting.com/AINV2020MFIC2023 when you enter your16-Digit control number. The Company is furnishing a proxy statement and proxy card to its stockholders on the Internet, rather than mailing printed copies of those materials to its stockholders. If you received a Notice of Internet Availability of Proxy Materials by mail, you will not receive a printed copy of the proxy statement and proxy card unless you request them. Instead, the Notice of Internet Availability of Proxy Materials will instruct you as to how you may access and review the proxy statement, and vote your proxy, on the Internet.

Whether or not you plan to participate in the Annual Meeting, we encourage you to vote your shares by following the instructions on the Notice of Internet Availability of Proxy Materials.

In the event there are not sufficient shares present for a quorum or sufficient votes to approve or ratify the proposals at the time of the Annual Meeting, the Annual Meeting may be adjourned in order to permit further solicitation of proxies by the Company.

APOLLO

MIDCAP FINANCIAL INVESTMENT CORPORATION

9 West 57th Street

New York, New York 10019

(212)515-3450

PROXY STATEMENT

20202023 Virtual Annual Meeting of Stockholders

This Proxy Statement is furnished in connection with the solicitation of proxies by the Board of Directors (the “Board”) of ApolloMidCap Financial Investment Corporation, a Maryland corporation (the “Company,” “we,” “us” or “our”), for use at the Company’s 20202023 Annual Meeting of Stockholders (the “Meeting”) to be held on Tuesday, August 11, 2020Monday, July 10, 2023 at 10:00 a.m., Eastern Daylight Time, virtually at www.virtualshareholdermeeting.com/AINV2020MFIC2023 and at any postponements or adjournments thereof. To participate in the Meeting virtually, you will need the Control Number included on your proxy card. Please note that those using thedial-in number for the listen-only conference call will not be able to vote or submit questions. This Proxy Statement, the Notice of Virtual Annual Meeting of Stockholders, the accompanying proxy card and the Company’s AnnualTransition Report on Form 10-KT for the fiscal yearnine-months ended MarchDecember 31, 2020,2022, will be made available to stockholders via the Internet on or about June 22, 2020.May 2, 2023.

We encourage you to access the Meeting prior to the start time. The live webcast and listen-only conference call will begin promptly at 10:00 a.m. Eastern Daylight Time. We will have technicians ready to assist you with any technical difficulties you may have accessing the live webcast or listen-only conference call. If you encounter any difficulties accessing the virtual meeting duringcheck-in or the meeting, please call the technical support number that will be posted on the virtual meeting platformlog-in page at www.virtualshareholdermeeting.com/AINV2020.MFIC2023. Technical support will be available starting at 9:30 a.m. on August 11, 2020July 10, 2023 and will remain available until thirty minutes after the Meeting has finished. The virtual meeting platform is fully supported across browsers (Internet Explorer,(Edge, Firefox, Chrome, and Safari) and devices (desktops, laptops, tablets, and cell phones) running the most updated version of applicable software and plugins. Participants should ensure that they have a strong WiFi connection wherever they intend to participate in the Meeting. Participants should also give themselves plenty of time todial-in to the conference call or log in and ensure that they can hear audio prior to the start of the Meeting.

We encourage you to vote your shares by following the instructions on the Notice of Internet Availability of Proxy Materials and granting a proxy (i.e., authorizing someone to vote your shares). If you provide voting instructions, either via the Internet, by telephone or by requesting, signing, dating and returning a proxy card, and the Company receives them in time for the Meeting, the persons named as proxies will vote your shares in the manner that you specified.If you give no instructions on the proxy card you execute, the shares covered by the proxy card will be voted FOR the election of the nominees as Directors and FOR the ratification of the Company’s independent registered public accounting firm.

You may revoke a proxy at any time before it is exercised by notifying the Company’s Secretary in writing, by submitting a properly executed later-dated proxy, or by participating in the virtual Meeting and voting online. Participating in the virtual Meeting does not revoke your proxy unless you also vote online at the Meeting.

If your shares are registered in the name of a bank, brokerage firm or other nominee, you will receive instructions from your bank, broker or other nominee that you must follow in order to instruct how your shares are to be voted at the Meeting.

If you want to submit a question during the Meeting, log into the live webcast atwww.virtualshareholdermeeting.com/AINV2020MFIC2023, type your question into the “Ask a Question” field, and click “Submit.”

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Only questions submitted via the live webcast that are pertinent to Meeting matters will be answered during the Meeting, subject to time constraints.Please note that no questions may be submitted via the listen-onlyconference call. Questions or comments that are not related to the proposals under discussion, are about personal concerns not shared by stockholders generally, or use blatantly offensive language may be ruled out of order. Additionally, the Company may not be able to answer multiple questions submitted by the same stockholder. Questions pertinent to Meeting matters that cannot be answered during the Meeting due to time constraints will be posted online and answered at www.virtualshareholdermeeting.com/AINV2020. The questions and answers will be available as soon as practicable after the Meeting and will remain available until one week after posting.MFIC2023.

Purpose of Meeting

At the Meeting, you will be asked to vote on the following proposals:

Voting Securities

You may vote your shares at the Meeting only if you were a stockholder of record at the close of business on June 12, 2020April 24, 2023 (the “Record Date”). There were 65,259,17665,451,359, shares of the Company’s common stock outstanding on the Record Date. Each share of common stock is entitled to one vote on each matter to be voted on at the Meeting. Stockholders do not have the right to cumulate votes in the election of directors.

Quorum Required

A quorum must be present at the Meeting for any business to be conducted. The presence at the Meeting, in person (virtually), or by proxy, of holders of shares of stock of the Company entitled to cast a majority of the votes entitled to be cast on the Record Date will constitute a quorum. Abstentions and brokernon-votes will be deemed to be present for the purpose of determining a quorum for the Meeting. Those stockholders accessing the Meeting via the listen-only conference call will not be deemed to be “present” for purposes of determining a quorum for the Meeting. If a stockholder of the Company does not vote electronically via the live webcast or does not submit voting instructions to its broker, bank or other nominee, the broker, bank or other nominee will not be permitted to vote the stockholder’s shares onnon-routine proposals. The ratification of the selection of PricewaterhouseCoopers LLPDeloitte as the Company’s independent registered public accounting firm for the year ending MarchDecember 31, 20212023 (Proposal 2) is considered routine under applicable rules. The election of directors (Proposal 1) is considerednon-routine under applicable rules. Fornon-routine proposals, a broker, bank or other nominee that holds shares in street name on behalf of a stockholder must receive voting instructions from the beneficial owner of the shares in order for the shares to be voted at the Meeting. A “brokernon-vote” with respect to a matter occurs when a broker, bank or other nominee holding shares on behalf of a beneficial owner has not received voting instructions from the beneficial owner on a particular proposal and does not have, or chooses not to exercise, discretionary authority to vote the shares on such proposals.Please note that to be sure your vote is counted on the Company’s proposal to elect directors, you should instruct your broker, bank, trustee or nominee how to vote your shares by following the voting instructions provided by your broker, bank, trustee or nominee. If you do not provide voting instructions, votes may not be cast on your behalf with respect to such proposal.

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nominee, your shares will not be voted with respect to the person indicated. Since Emanuel Pearlman is currently a Class III Director, if he is not elected as a Class I Director at the Meeting, he will continue to serve as a Class III Director until the Annual Meeting of Stockholders in 2025. Because Directors are elected by an affirmative vote of the majority of the total votes cast for and affirmatively withheld, votes to withhold authority will have the effect of a vote against a nominee. Brokernon-votes will not be included in determining the number of votes cast and as a result will have no effect on this proposal.

Ratification of Independent Registered Public Accounting Firm.The affirmative vote of a majority of the votes cast at the Meeting virtually or by proxy is required to ratify the appointment of PricewaterhouseCoopers LLP (“PricewaterhouseCoopers”)Deloitte to serve as the Company’s independent registered public accounting firm for the fiscal year ending MarchDecember 31, 2021.2023. Abstentions and brokernon-votes, if any, will not be included in determining the number of votes cast and as a result will have no effect on this proposal.

Additional Solicitation.If there are not enough shares represented at the Meeting for a quorum or votes to approve or ratify a proposal at the Meeting, the Executive Chairman of the Meeting may adjourn the Meeting to permit the further solicitation of proxies.

A stockholder vote may be taken on any proposal in this Proxy Statement prior to any such adjournment if a quorum is present and there are sufficient votes for approval of such proposal.

Authorizing a Proxy for Shares Held in Your Name

If you are a record holder of shares of the Company’s common stock, you may authorize a proxy to vote on your behalf by following the instructions provided on the Notice of Internet Availability of Proxy Materials. Authorizing your proxy will not limit your right to participate in the virtual Meeting and vote your shares online. A properly completed and submitted proxy will be voted in accordance with your instructions unless you subsequently revoke your instructions. If you authorize a proxy without indicating your voting instructions, the proxyholder will vote your shares according to the Board’s recommendations. Internet and telephone voting procedures are designed to authenticate the stockholder’s identity and to allow stockholders to vote their shares and confirm that their instructions have been properly recorded. Your Internet or telephone vote authorizes the named proxies to vote your shares in the same manner as if you had marked, signed and returned a proxy card.

Revoking Your Proxy

If you are a stockholder of record, you can revoke your proxy at any time before it is exercised by: (i) delivering a written revocation notice that is received prior to the Meeting to ApolloMidCap Financial Investment Corporation at 9 West 57th Street, New York, New York 10019, Attention: Secretary; (ii) submitting a later-dated proxy that we receive before the conclusion of voting at the Meeting; or (iii) participating in the virtual Meeting and voting online. If you hold shares of a Company’s common stock through a broker, bank, trustee or nominee, you must follow the instructions you receive from them in order to revoke your voting instructions. Participating in the virtual Meeting does not revoke your proxy unless you also vote online at the Meeting.

Information Regarding This Solicitation

The Company will bear the expense of the solicitation of proxies for the Meeting. The Company has retained Georgeson LLC (“Georgeson”) to assist in the solicitation of proxies. The Company expects to pay market rates for such services, with an estimated fee of approximately $8,500, plus expenses. As the Meeting date approaches, certain stockholders of the Company may receive a telephone call from a representative of

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In all cases where a telephonic proxy is solicited, the Georgeson representative is required to ask each stockholder to confirm his or her full name and to confirm a portion of the address that appears on the stockholder’s account registration. The Georgeson representative will ask the stockholder to confirm that he or she has either received the proxy materials in the mail or has been provided a notice and access notification. If the stockholder is a corporation or entity, the Georgeson representative is required to ask for the person’s title and confirmation that the person is authorized to direct the voting of the shares. If the information solicited matches the information provided to Georgeson, then the Georgeson representative has the responsibility to explain the process, read the proposals listed on the proxy card and ask for the stockholder’s instructions on the proposals. Although the Georgeson representative is permitted to answer questions about the process, he or she is not permitted to recommend to the stockholder how to vote, other than to read any recommendation set forth in this Proxy Statement. Georgeson will record the stockholder’s instructions electronically and submit the instructions electronically to be tabulated. The stockholder will be sent a letter to confirm his or her proxy authorization and provide instructions for making corrections if his or her voting instructions are not correctly reflected in the confirmation.

We have requested that brokers, nominees, fiduciaries and other persons holding shares in their names, or in the names of their nominees, which are beneficially owned by others, forward the proxy materials to, and obtain proxies from, such beneficial owners. We will reimburse such persons for their reasonable expenses in so doing.

In addition to mail and email, proxies may be solicited personally via the Internet or by telephone or facsimile transmission by directors or officers of the Company or officers or employees of Apollo Investment Management, L.P. (“AIM”), our investment adviser (“AIM” or the “Investment Adviser”) (without special compensation). AIM is located at 9 West 57th Street, New York, New York 10019.

Security Ownership of Certain Beneficial Owners and Management

As of the Record Date, to our knowledge, no person would be presumed under the Investment Company Act of 1940, as amended (the “1940 Act”), to “control” us, as such term is defined in the 1940 Act.

Our Directors consist of independent Directors (Directors who are not “interested persons” (as defined in the 1940 Act) of the Company, and therefore not affiliates of AIM) (“Independent Directors”) and interestedInterested Directors. Interested Directors are “interested persons” of the Company, as defined in the 1940 Act.

The following table sets forth, asAs of March 31, 2020, certain ownership information with respect to our common stock for those persons whom we believe,the Record Date, based on public filings and/or information, provided by such persons,we believe that no stockholder, directly or indirectly owned, controlled or held, with the power to vote, 5% or more of our outstanding common stock as of that date as well asdate. The following table sets forth our affiliates that directly or indirectly owned, controlled or held, with the power to vote, our outstanding common stock as of that date.the Record Date. Unless otherwise indicated, we believe that each beneficial owner set forth in the table has sole voting and investment power over the securities owned by it.

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Officers. As of that date, the Company’s Directors and Executive Officers, as a group, owned less than 1% of the Company’s outstanding common stock.

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Dollar Range of Securities Beneficially Owned by Directors

The following table sets forth the dollar range of our common stock beneficially owned by the Director nominees and each of our other Directors as of the Record Date. Information as to the beneficial ownership is based on information furnished to the Company by such persons. (We are not part of a “family of investment companies” as that term is defined in the 1940 Act).

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PROPOSAL 1: ELECTION OF DIRECTORS

Pursuant to the Company’s charter and bylaws, the Board of Directors may modify the number of members of the Board of Directors provided that the number thereof shall never be less than four nor more than ten. In accordance with the bylaws, at the conclusion of this Meeting, the Company will have eightcurrently has nine members ofon the Board of Directors. Directors are divided into three classes and are generally elected for staggered terms of three years each, with a term of office of one of the three classes of Directors expiring each year. The Company may have cause to propose a term of less than three years for a Director as it may deem necessary. Each Director will hold office for the term to which he or she is elected or until his or her successor is duly elected and qualified.

A stockholder can vote for, or withhold his or her vote from, any nominee. In the absence of instructions to the contrary, it is the intention of the persons named as proxies to vote such proxy FOR the election of the nominees named below. If a nominee should decline or be unable to serve as a Director, it is intended that the proxy will be voted for the election of such person as is nominated by the Board of Directors as a replacement. The Board of Directors has no reason to believe that any of the persons named below will be unable or unwilling to serve.

THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT YOU VOTE FOR THE ELECTION OF THE NOMINEES NAMED IN THIS PROXY STATEMENT.

Information about the Nominees and Directors

Certain information with respect to the Class I nominees for election at the Meeting, as well as each of the other Directors who are not standing forre-election, is set forth below, including their names, ages, a brief description of their recent business experience, including present occupations and employment, certain directorships that each person held during the last five years, and the year in which each person became a Director of the Company.

On January 3, 2020, James Zelter notifiedMarch 8, 2023, the Company that he would resignBoard of Directors appointed Emanuel Pearlman to the Board to serve as a Class III Director of the Company effective immediately.Company. On May 20, 2020, Carl Spielvogel announced that he will be resigning fromApril 28, 2023, Jeanette Loeb and Frank Puleo informed the Board effective asof Directors that they have decided not to stand for re-election to the Board at the end of their current term and, therefore, will not stand for re-election at the Meeting. In connection with Ms. Loeb and Mr. Puleo’s departures, the Board determined that, in accordance with Article 4, Section 4.1 of the conclusionArticles of Restatement of the Meeting. NeitherCompany, it was in the best interest of the Company to re-assign Mr. Zelter’s or Mr. Spielvogel’s decisionPearlman to resign was a resultClass I, such that the directors are divided as evenly as reasonably possible into the three classes. Accordingly, the Board of any disagreement with the Company.

Jeanette W. Loeb, Frank C. Puleo, andDirectors has nominated Howard T. Widra each has been nominated for electionand Emanuel Pearlman to serve as a Class I Director for a three-year term expiring at the Company’s 20232026 Annual Meeting of Stockholders and until their successors are duly elected and qualified. Ms. Loeb and Messrs. Puleo andSince Emanuel Pearlman is currently a Class III Director, if he is not elected as a Class I Director at the Meeting, he will continue to serve as a Class III Director until the Annual Meeting of Stockholders in 2025. Mr. Widra currently serveserves as Directorsa Class I Director of the Company. None of Ms. Loeb and Messrs. PuleoPearlman and Widra isare being proposed for election pursuant to any agreement or understanding between Ms. Loeb and Messrs. PuleoPearlman and Widra and the Company.

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Nominees for Class I Directors—Term Expiring 20232026

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CONTINUING DIRECTORS (not up for election at the Meeting)

Nominees for Class III Directors—Term Expiring 20222025

Corporate Governance

Director Independence. NASDAQ rules require listed companies to have a board of directors with at least a majority of Independent Directors. Under NASDAQ rules, in order for a director to be deemed independent, the board of directors must determine that the individual does not have a relationship that would interfere with the director’s exercise of independent judgment in carrying out his or her responsibilities. On an annual basis, each member of our Board of Directors is required to complete an independence questionnaire designed to provide information to assist the Board of Directors in determining whether the Director is independent under NASDAQ rules and our corporate governance guidelines. Our Board of Directors has determined that each of our Directors, other than Messrs. Hannan Wechsler and Widra isand Ms. Whonder, are independent under the listing standards of NASDAQ Marketplace Rule 5605 (a)(2). Our governance guidelines require any Director who has previously been determined to be independent to inform the Executive Chairman of the Board of Directors, the Chairman of the Nominating and Corporate Governance Committee and our Corporate Secretary of any change in circumstance that may cause his or her status as an Independent Director to change. The Board of Directors limits membership on the Audit Committee and the Nominating and Corporate Governance Committee to Independent Directors.

Board of Directors’ Oversight Role in Management.The Board of Directors’ role in management of the Company is oversight. As is the case with virtually all investment companies, including externally managed

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Audit Committee Chair maintains contact with the Company’s independent registered public accounting firm, the Company’s Chief Financial Officer and the internal auditor. In addition, at its quarterly meetings, the Audit Committee meets with the independent valuation services that evaluate certain of the Company’s securities holdings for which there are not readily available market values. The Board of Directors also receives periodic presentations from senior personnel of AIM or its affiliates regarding risk management generally, as well as periodic presentations regarding specific operational, compliance or investment areas such as business continuity, personal trading, valuation, credit and investment research. The Board of Directors has adopted policies and procedures designed to address certain risks of the Company. In addition, the Company, AIM, AIA and other service providers to the Company have adopted a variety of policies, procedures and controls designed to address particular risks to the Company. However, it is not possible to eliminate all of the risks applicable to the Company. The Board of Directors also receives reports from counsel to the Company or counsel to AIM and the Board of Directors’ own independent legal counsel regarding regulatory compliance and governance matters. The Board of Directors oversight role does not make the Board of Directors a guarantor of the Company’s investments or activities or the activities of any of the Company’s service providers on behalf of the Company.

Board of Directors Composition and Leadership Structure.The 1940 Act requires that at least a majority of the Company’s Directors be Independent Directors. Currently, six of the Company’s eight continuingnine Directors are Independent Directors. The Executive Chairman and Vice Chairman of the Board of Directors is anare interested personpersons of the Company, and the Independent Directors have designated a lead Independent Director, Mr. Stein, who chairs meetings or executive sessions of the Independent Directors, reviews and comments on Board of Directors meeting agendas, represents the views of the Independent Directors to management and facilitates communication among the Independent Directors and their counsel and between management and the Independent Directors. The Board of Directors has determined that its leadership structure, in which over 60% of the Directors are not affiliated with AIM, is appropriate in light of the services that AIM and its affiliates provide to the Company and potential conflicts of interest that could arise from these relationships.

Information About Each Director’s Experience, Qualifications, Attributes or Skills. Additional information about each Director follows (supplementing the information provided in the table above) that describes some of the specific experiences, qualifications, attributes or skills that each Director possesses which the Board of Directors believes has prepared them to be effective Directors. The Board of Directors believes that the significance of each Director’s experience, qualifications, attributes or skills is an individual matter (meaning that experience that is important for one Director may not have the same value for another) and that these factors are best evaluated at the board level, with no single Director, or particular factor, being indicative of board effectiveness. However, the Board of Directors believes that Directors need to have the ability to critically review, evaluate, question and discuss information provided to them, and to interact effectively with Company management, service providers and counsel, in order to exercise effective business judgment in the performance of their duties; the Board of Directors believes that its members satisfy this standard. Experience relevant to having this ability may be achieved through a Director’s educational background; business, professional training or practice (e.g., medicine, accounting or law), public service or academic positions; experience from service as a board member (including the Board of Directors of the Company) or as an executive of investment funds, public companies or significant private ornot-for-profit entities or other organizations; and/or other life experiences. To

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pharmacy that sells pet medications, supplies and food directly to the consumer. Ms. Loeb has served as Chief Executive Officer of PetCareRx since 2015 and formerly served as Chairman and Chief Executive Officer of the company from 2001 to 2011. From 1977 until 1994, Ms. Loeb was an investment banker at Goldman Sachs & Co., where she served as the head of the Structured Finance Department in the U.S. Ms. Loeb was named the first woman partner of Goldman Sachs & Co. in 1986 and served as a partner from 1986 to 1994. Ms. Loeb received an MBA from Harvard Business School and graduated Phi Beta Kappa from Wellesley College with a BA in economics. She currently serves on the board and the finance committee of New York City Center and also serves on the board, governance and audit committees of the AB Funds. She has previously been on the board and audit committee of the United Nations Development Corporation, the board for Alliance Bernstein Multi-Manager Alternative Fund, a member of the board of the Collegiate School, the Treasurer and a board member of the Society of Memorial Sloan Kettering, and a founding member of the Wellesley Business Leadership Council.

Barbara Matas (60)(62) Director. Ms. Matas became a Director of the Company in March 2017. Ms. Matas formerly served as the Chairman of Citigroup’s Leveraged Finance business from 2013 to 2016 andCo-Head from 2006 to 2013. Ms. Matas joined Citicorp in 1985 and held various leadership positions in leveraged finance and high yield capital markets at Citicorp, Salomon Brothers and Citigroup until 2006. She began her career as an auditor at Touche Ross. Ms. Matas has also been a directorDirector of Sleep Number since 2016.2016 and a Director of BRP Group, Inc. since February 2020. Ms. Matas holds a B.S. in accounting and quantitative analysis from New York University and an M.B.A. in corporate finance from the University of Michigan.

Frank C. Puleo(74)(76) Director. Mr. Puleo became a Director of the Company in February 2008. Mr. Puleo currently serves as a Director of South Street Holdings, LLC (formerly known as CMET Finance Holdings, Inc.), a company that finances securities inventory for customers and dealers and licenses trade processing software and SLM Corp., a student loan company, and Syncora Holdings Ltd.company. From 2006 to 2014, Mr. Puleo was a Director of CIFC Corp. (formerly known as CIFC Deerfield Corp.), a credit asset manager. Previously, Mr. Puleo was also a partner at Milbank, Tweed, Hadley & McCloy LLP (“Milbank”) where he advised clients on structured finance transactions, bank and bank holding company regulatory and securities law matters. Mr. Puleo became a partner of Milbank in 1978 andCo-Chair of its Global Finance Group in 1995 until retiring at the end of 2006. He was a member of the Milbank’s Executive Committee from 1982 to 1991 and from 1996 to 2002. Mr. Puleo served as a Lecturer at Columbia University School of Law from 1997 to 2001.

Emanuel Pearlman (63) Director. Mr. Pearlman became a Director of the Company in March 2023. Mr. Pearlman is the Founder, Chairman and Chief Executive Officer of Liberation Investment Group, an investment management and consulting firm that provides financial consulting, devises capital structures, negotiates IPOs, leads acquisitions and mergers, implements restructurings, and creates other complex financial plans for variety of companies. In February 2023, Mr. Pearlman became a member of the Board of Diebold Nixdorf, Inc., a multinational financial and retail technology company that specializes in the sale, manufacture, installation and service of self-service transaction systems (such as ATMs and currency processing systems), point-of-sale terminals, physical security products, and software and related services for global financial, retail and commercial markets. In March 2023, Manny became a member of the Board of QualTek Services, Inc. (NASDAQ:QTEK) a turnkey provider of infrastructure services and renewable energy project solutions to the North American telecommunications and power industries. He is a member of the Special Committee established to review and approve strategic and financial alternatives. He also serves as a member of the Finance and the People & Compensation Committees. Since January 2012, Mr. Pearlman has been a director of Network-1 Technologies, Inc., a company specializing in the development, licensing, and protection of its intellectual property assets, where he serves as chairman of the audit committee and a member of the nominating and governance committee. Mr. Pearlman is currently a director of LSC Communications, LLC, the largest producer of books in the United States and a leading manufacturer and distributor of magazines, catalogs and office products, serving as a member of the audit and compensation committees since 2021. From March 2022 to April 2022, Mr. Pearlman served as a director of Redbox Entertainment, Inc., an entertainment company, and chair of its strategic review committee. In October 2020 and February 2021, Mr. Pearlman became a director of Atlas Crest Investment Corp. and Atlas Crest Investment Corp. II, special purpose acquisition companies. He served as

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chairman of the audit committee and a member of the compensation committee and nomination & governance committee on both boards until his ACIC board service ended in September 2021 and his ACII board service ended in June 2022. Prior to that, Mr. Pearlman served as director of Empire Resorts, Inc. (2010 - 2019); CEVA Logistics, AG (2018-2019); CEVA Holdings, LLC (2013-2018); ClubCorp Holdings, Inc. (2017); Fontainebleau Miami JV, LLC (2009-2014); Jameson Inns, Inc. (2012); Dune Energy, Inc. (2012-2013); Multimedia Games, Inc. (2006-2010); and Network-1 Security Solutions, Inc. (2000-2002). Mr. Pearlman holds an M.B.A. from Harvard Business School and an A.B. from Duke University.

R. Rudolph Reinfrank(64)(67) DirectorDirector.. Mr. Reinfrank became a Director of the Company in June 2013. Mr. Reinfrank also currently serves as a Senior Advisor to BC Partners,board member of Mount Logan Capital, a leading international investment firmCanada-based asset manager and Grafine Partners, an asset management firm.as a board member of Perception Capital II, a special purpose acquisition company. Mr. Reinfrank recently served as a Director of Kayne Anderson Acquisition Corp. and chaired its audit and conflict committees. Since October 2009, Mr. Reinfrank has served as the Managing General Partner of Riverford Partners, LLC, a strategic advisory and investment firm based in Los Angeles. Riverford Partners acts as an investor, board member and strategic adviser to growth companies and companies in transition. In 2000, Mr. Reinfrankco-founded and served as a Managing General Partner of Clarity Partners, L.P. until 2009. In 1997, heco-founded and serves as a Managing General Partner of Rader Reinfrank & Co. In 2006, heco-founded Clarity China, L.P. Mr. Reinfrank is also a Senior Adviseran advisor or board member to Pall Mall Capital, Limited (London) and Transnational Capital Corporation (NYC).several privately held companies.

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a diploma from the Universidad Pontificia de Salamanca and a Masters in International Public Policy from Johns Hopkins University School of Advanced International Studies. Ms. Whonder was nominated to serve as a director on theour board of Math for Americadirectors because of her significant professional experience and is a member ofexpertise in public policy in the Academy of Motion Picture Artsfinancial services and Sciences.housing sector.

Howard T. Widra (51)(54)Chief Executive OfficerChairman and Director.Mr..Mr. Widra has been with Apollo Global Management, LLCInc. and/or its affiliates (“AGM”) since 2013.2013 and serves as AGM’s Head of Direct Origination. He became the Chief Executive and a Director of ApolloMidCap Financial Investment Corporation in May 2018 and previously served as the Company’s President sincefrom June 2016.2016 to May 2018. Mr. Widra iswas a co-founder of MidCap Financial (“MidCap”), a middle market specialty finance business with $9 billion of funds employed and $28 billion of commitments under management,firm, and was formerly its Chief Executive Officer. Prior to MidCap, Mr. Widra was the founder and President of Merrill Lynch Capital Healthcare Finance. Prior to Merrill Lynch, Mr. Widra was President of GE Capital Healthcare Commercial Finance and held senior roles in its predecessor entities including President of Heller Healthcare Finance, and COO of Healthcare Financial Partners. Mr. Widra holds a J.D., Cum Laude, from the Harvard Law School and a BAB.A. from the University of Michigan.

Committees of the Board of Directors

As of MarchDecember 31, 2020,2022, our Board of Directors had established an Audit Committee, a Nominating and Corporate Governance Committee and a Compensation Committee. For the fiscal yearnine-months ended MarchDecember 31, 2020,2022, the Board of Directors of the Company held 2410 board meetings, eight Audit Committee meetings, four Nominating and Corporate Governance Committee meetings and one Compensation Committee meeting.

The Company requires each Director to make a diligent effort to attend all Board of Directors and committee meetings, and encourages Directors to attend the annual meeting of stockholders. At the 20192022 Annual Meeting, all of the Directors attended in person.virtually.

Audit Committee.The Audit Committee operates pursuant to an Audit Committee Charter approved by the Board of Directors. The charter sets forth the responsibilities of the Audit Committee, which include selecting or

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management; and undertaking such other duties and responsibilities as may from time to time be delegated by the Board of Directors to the Nominating and Corporate Governance Committee. The Nominating and Corporate Governance Committee is composed of each of the Independent Directors, whom, after the Meeting are: Messrs. Puleo, Pearlman, Reinfrank and Stein and Mses. Matas and Loeb. Mr. Stein currently serves as the Chairman of the Nominating and Corporate Governance Committee. The Nominating and Corporate Governance Committee has adopted a written Nominating and Corporate Governance Committee charter which is available on the Company’s website (http://www.apolloic.comwww.midcapfinancialic.com).

The Nominating and Corporate Governance Committee will consider stockholder recommendations for possible nominees for election as Directors when such recommendations are submitted in accordance with the Company’s current bylaws, the Nominating and Corporate Governance Committee Charter and any applicable law, rule or regulation regarding Director nominations. Nominations should be sent to Joseph D. Glatt,Kristin Hester, Corporate Secretary, ApolloMidCap Financial Investment Corporation, 9 West 57^th Street, New York, New York 10019. To have a candidate considered by the Nominating and Corporate Governance Committee, a stockholder must submit the recommendation in writing and must include the following information:

Criteria considered by the Nominating and Corporate Governance Committee in evaluating the qualifications of individuals for election as members of the Board of Directors include, to the extent required, compliance with the independence and other applicable requirements of the federal securities laws, the listing standards of NASDAQ, and any other applicable laws, rules, or regulations; the ability to contribute to the

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Puleo, Reinfrank and Stein and Mses. Matas and Loeb, each of whom is not an interested person of us for purposes of the 1940 Act and the NASDAQ corporate governance rules. As shown below, none of our executive officers is directly compensated by us and, as a result, the Compensation Committee does not produce and/or review and report on executive compensation practices. The Compensation Committee Charter is available on our website (www.apolloic.com)(www.midcapfinancialic.com).

Co-Investment Committee. TheCo-Investment Committee is responsible for reviewing and approving certainco-investment transactions pursuant to the exemptive order we received from the Securities and the Commission on March 29, 2016, which was amended on January 10, 2023 (the “Order”). TheCo-Investment Committee is comprised of all the Independent Directors.

Communication with the Board of Directors

Stockholders with questions about the Company are encouraged to contact the Company’s Investor Relations Department. However, if stockholders believe that their questions have not been addressed, they may communicate with the Company’s Board of Directors by sending their communications to ApolloMidCap Financial Investment Corporation, c/o Joseph D. Glatt,Kristin Hester, Corporate Secretary, 9 West 57^th Street, New York, New York 10019. All stockholder communications received in this manner will be delivered to one or more members of the Board of Directors.

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Compensation of Directors

Each Independent Director’s annual fee is $135,000.$145,000. Each Independent Director also receives $2,500 plus reimbursement of reasonableout-of-pocket expenses incurred in connection with attending each Board meeting, $1,000 plus reimbursement of reasonableout-of-pocket expenses incurred in connection with each committee

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Delinquent Section 16(a) Reports

Pursuant to Section 16(a) of the Exchange Act, the Company’s Directors and other executive officers, and any persons holding more than 10% of its common stock, are required to report their beneficial ownership and any changes therein to the SEC and the Company. Specific due dates for those reports have been established, and the Company is required to report in this proxy statement any failure to file such reports by those due dates. Based on the Company’s review of Forms 3, 4 and 5 filed by such persons and information provided by the Company’s Directors and other executive officers, the Company believes that during the fiscal year ended December 31, 2022, all Section 16(a) filing requirements applicable to such persons were met in a timely manner with the exception of the initial Form 3 filing for Carmencita Whonder, which was filed late due to administrative oversight. For the period from January 1, 2023 through the date of this proxy statement, the Company believes that all Section 16(a) filing requirements were met in a timely manner with the exception of one late Form 4 filing for John Hannan reporting a transaction on November 15, 2021, which, when filed, will be late due to administrative oversight.

Certain Relationships and Transactions

Transactions with Affiliated Persons. We have entered into an amended and restated investment advisory and management agreement with AIM. Certain of our Executive Officers and our Chairman of the Board of Directors have ownership and financial interests in AIM. Certain of our Executive Officers also serve as principals of other investment managers affiliated with AIM that may in the future manage investment funds with investment objectives similar to ours. In addition, our Executive Officers and Directors and the partners of our investment adviser, AIM, serve or may serve as officers, directors or principals of entities that operate in the same or related line of business as we do, or of investment funds managed by its affiliates, although we may not be given the opportunity to participate in certain investments made by investment funds managed by advisers affiliated with AIM. However, our investment adviser and its affiliates intend to allocate investment opportunities in a fair and equitable manner consistent with our investment objectives and strategies so that we are not disadvantaged in relation to any other client. We may invest, to the extent permitted by law, on a concurrent basis with affiliates of AIM, subject to compliance with applicable regulations and our allocation procedures.

We have entered into a royalty-free license agreement with Apollo Management Holdings, L.P. (“AMH”),AGM, pursuant to which AMHAGM has agreed to grant us anon-exclusive license to use the name “Apollo.” Under the license agreement, we have the right to use the “Apollo” name for so long as AIM or one of its affiliates remains our investment adviser. In addition, we rent office space from AIA, an affiliate of AIM, and pay AIAApollo Administration our allocable portion of overhead and other expenses incurred by AIA in performing its obligations under our administration agreement with AIA, including our allocable portion of the cost of our Chief Financial Officer, and Chief Compliance Officer, Chief Legal Officer and their respective staffs, which can create conflicts of interest that our Board of Directors must monitor.

On August 1, 2022, the Company changed its name from “Apollo Investment Corporation” to “MidCap Financial Investment Corporation”. As a result, we have entered into a trademark license agreement with Apollo Capital Management, L.P., which grants us a non-exclusive license to use the name “MidCap Financial.”

With respect to Director independence, please refer to the Corporate Governance section herein.

Section 16(a) Beneficial Ownership Reporting Compliance. Pursuant to Section 16(a) of the Exchange Act, the Company’s Directors and Executive Officers, and any persons holding more than 10% of its common stock, are required to report their beneficial ownership and any changes therein to the Commission. Specific due dates for those reports have been established, and the Company is required to report herein any failure to file such reports by those due dates. Based on the Company’s review of Forms 3, 4 and 5 filed by such persons and information provided by the Company’s Directors and officers, the Company believes that during the fiscal year ended March 31, 2020, except for one filing, all Section 16(a) filing requirements applicable to such persons were met in a timely manner. Due to administrative oversights, Tanner Powell did not file a Form 4 on a timely basis.

THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT YOU VOTE FOR THE ELECTION OF THE NOMINEES NAMED IN THIS PROXY STATEMENT.

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PROPOSAL II: RATIFICATION OF

SELECTION OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

At a meeting held on May 20, 2020,On April 26, 2023 the Company’s Audit Committee approved and the Board of Directors, including a majority of the Independent Directors, approved and ratified the selection of PricewaterhouseCoopersDeloitte as the Company’s independent registered public accounting firm for the fiscal year ending MarchDecember 31, 2021.2023. The Company expects that a representative of PricewaterhouseCoopersDeloitte will be present virtually at the Meeting, and will have an opportunity to make a statement (if the representative so desires) and to respond to appropriate questions. PricewaterhouseCoopers LLP (“PricewaterhouseCoopers”) served as the Company’s independent registered public accounting firm for the fiscal year ending March 31, 2022. After reviewing the Company’s audited financial statements for the fiscal yearnine-months ended MarchDecember 31, 2020,2022, the Board of Directors’ Audit Committee recommended to the Board of Directors that such statements be included in the Company’s AnnualTransition Report on Form10-K.10-KT. A copy of the Audit Committee’s Report appears below.

Change in Accounting Firm

On March 8, 2022, the Independent Directors of the Company, upon the recommendation of the audit committee, dismissed PricewaterhouseCoopers as the Company’s independent registered public accounting firm for the Company’s fiscal year ending March 31, 2023, effective upon the completion the audit of the Company’s financial statements as of and for the year ending March 31, 2022. On November 3, 2022, the Company changed its fiscal year end to December 31, 2022.

The reports of PricewaterhouseCoopers on the Company’s financial statements for the fiscal year ended March 31, 2021, and the subsequent period through March 8, 2022, did not contain an adverse opinion or a disclaimer of opinion, nor were they qualified or modified as to uncertainty, audit scope or accounting principles.

In connection with the audits of the Company’s financial statements for the fiscal year ended March 31, 2021, and the subsequent period through March 8, 2022, there were no “disagreements” (as defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions) between the Company and PricewaterhouseCoopers on any matter of accounting principles or practices, financial statement disclosure or auditing scope or procedures, which, if not resolved to the satisfaction of PricewaterhouseCoopers, would have caused PricewaterhouseCoopers to make reference to the subject matter of the disagreement in connection with its report. During the fiscal year ended March 31, 2021 and the interim period through March 8, 2022, there were no “reportable events” (as that term is defined in Item 304(a)(1)(v) of Regulation S-K).

The Company provided PricewaterhouseCoopers with a copy of the disclosures contained in the Company’s Current Report on Form 8-K filed on March 11, 2022 and requested PricewaterhouseCoopers furnish the Company with a letter addressed to the U.S. Securities and Exchange Commission stating whether it agrees with the disclosures. A copy of PricewaterhouseCoopers’s letter, dated March 11, 2022, is filed as Exhibit 16.1 to the Company’s Current Report on Form 8-K filed with the SEC on March 11, 2022.

On March 8, 2022, the Board of Directors of the Company, upon the recommendation of the audit committee, approved a resolution appointing Deloitte as the Company’s independent registered public accounting firm for the Company’s fiscal year ending March 31, 2023, subject to the approval of the Company’s shareholders. The engagement of Deloitte is subject to Deloitte’s client acceptance procedures and execution of an engagement letter.

During the fiscal year ended March 31, 2021, and the interim period through March 8, 2022, the Company did not, nor did anyone on the Company’s behalf, consult with Deloitte regarding (a) the application of accounting principles to a specified transaction, either completed or proposed, or the type of audit opinion that might be rendered on the Company’s financial statements, and no written report or oral advice was provided to

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the Company that Deloitte concluded was an important factor considered by the Company in reaching a decision as to any accounting, auditing or financial reporting issue or (b) any matter that was either the subject of a disagreement (as defined in Item 304(a) (1)(iv) of Regulation S-K and the related instructions) or a reportable event (as described in Item 304(a)(1)(v) of Regulation S-K).

Fees Paid

Audit Fees: Audit fees consist of fees billed for professional services rendered for the audit of ouryear-end financial statements and services that arewere normally provided by Deloitte and PricewaterhouseCoopers in connection with statutory and regulatory filings. Audit fees billed during the nine-months ended December 31, 2022 and the fiscal yearsyear ended March 31, 20202022 were $1,380,000 and March 31, 2019 were $1,345,000 and $1,300,000,$838,257 respectively.

Audit-Related Fees: Audit-related services consist of fees billed by Deloitte and PricewaterhouseCoopers for assurance and related services that are reasonably related to the performance of the audit or review of our financial statements and are not reported under “Audit Fees.” These services include attest services that are not required by statute or regulation and consultations concerning financial accounting and reporting standards. Audit-related fees billed during the nine-months ended December 31, 2022 and the fiscal yearsyear ended March 31, 20202022 were $0 and March 31, 2019 were $71,810 and $71,395,$71,688, respectively.

Tax Services Fees: Tax services fees consist of fees billed by Deloitte and PricewaterhouseCoopers for professional tax services. These services also include assistance regarding federal, state, and local tax compliance. Tax services and fees billed during the nine-months ended December 31, 2022 and the fiscal yearsyear ended March 31, 20202022 were $116,350 and March 31, 2019 were $100,000 and $80,850,$304,500, respectively, which represented work related to, among other things, preparation of tax returns, our regulated investment company (RIC) qualification, excise tax distribution requirements and form extensions.

All Other Fees: Other fees would include fees billed by Deloitte and PricewaterhouseCoopers for products and services other than the services reported above, of which there were none induring the nine-months ended December 31, 2022 and the fiscal yearsyear ended March 31, 2020 and March 31, 2019.2022.

Audit Committee Pre-Approval Policy

The Audit Committee has established apre-approval policy that describes the permitted audit, audit-related, tax and other services to be provided by PricewaterhouseCoopers,Deloitte, the Company’s auditors. The policy requires that the Audit Committeepre-approve the audit andnon-audit services performed by the auditors in order to assure that the provision of such service does not impair the auditors’ independence.

Any requests for audit, audit-related, tax and other services that have not received generalpre-approval must be submitted to the Audit Committee for specificpre-approval, and cannot commence until such approval has been granted. Normally,pre-approval is provided at regularly scheduled meetings of the Audit Committee. However, the Audit Committee may delegatepre-approval authority to one or more of its members. The member or members to whom such authority is delegated reports anypre-approval decisions to the Audit Committee at its next scheduled meeting. The Audit Committee does not delegate its responsibilities topre-approve services performed by the independent auditor to management.

All services described above under “Audit-Related Fees” and “Tax Services Fees” werepre-approved by the Audit Committee.

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The Audit Committee has reviewed and discussed the Company’s audited financial statements with management and PricewaterhouseCoopers LLP,Deloitte, the Company’s independent registered public accounting firm for the nine-months ended December 31, 2022, with and without management present. The Audit Committee included in its review results of PricewaterhouseCoopers LLP’sDeloitte’s examinations, the Company’s internal controls, and the quality of the Company’s financial reporting. The Audit Committee also reviewed the Company’s procedures and internal control processes designed to ensure full, fair and adequate financial reporting and disclosures, including procedures for certifications by the Company’s chief executive officer and chief financial officer that are required in periodic reports filed by the Company with the Commission. The Audit Committee is satisfied that the Company’s internal control system is adequate and that the Company employs appropriate accounting and auditing procedures.

The Audit Committee also has discussed with PricewaterhouseCoopers LLPDeloitte matters relating to PricewaterhouseCoopers LLP’sDeloitte’s judgments about the quality, as well as the acceptability, of the Company’s accounting principles as applied in its financial reporting as required by the Statement on Auditing Standards No. 1301 as amended (Communications with Audit Committee). In addition, the Audit Committee has discussed with PricewaterhouseCoopers LLPDeloitte their independence from management and the Company, as well as the matters in the written disclosures received from PricewaterhouseCoopers LLPDeloitte and required by Statement on Auditing Standard No. 114, as amended (Codificationapplicable requirements of Statements on Auditing Standards, AU Section 380, as adopted by the Public Company Accounting Oversight Board in Rule 3200T), Public Company Accounting Oversight Board Rule 3526, “Communication with Audit Committees Concerning Independence”.PCAOB and the SEC. The Audit Committee received a letter from PricewaterhouseCoopers LLPDeloitte confirming their independence and discussed it with them. The Audit Committee discussed and reviewed with PricewaterhouseCoopers LLPDeloitte the Company’s critical accounting policies and practices, internal controls, other material written communications to management, and the scope of PricewaterhouseCoopers LLP’sDeloitte audits and all fees paid to PricewaterhouseCoopers LLPDeloitte during the fiscal year.nine-months ended December 31, 2022. The Audit Committee has adopted guidelines requiring review andpre-approval by the Audit Committee of audit andnon-audit services performed by PricewaterhouseCoopers LLPDeloitte for the Company. The Audit Committee has reviewed and considered the compatibility of PricewaterhouseCoopers LLP’sDeloitte’s performance ofnon-audit services with the maintenance of PricewaterhouseCoopers LLP’sDeloitte’s independence as the Company’s independent registered public accounting firm.

Based on the Audit Committee’s review and discussions referred to above, the Audit Committee recommended to the Board of Directors (and the Board of Directors has approved) that the Company’s audited financial statements be included in the Company’s AnnualTransition Report on Form10-K10-KT for the fiscal yearnine-months ended MarchDecember 31, 20202022 for filing with the Commission. In addition, the Audit Committee has engaged PricewaterhouseCoopers to serve as the Company’s independent registered public accounting firm for the fiscal year ending March 31, 2020, and has directed that the selection of PricewaterhouseCoopers LLP be submitted to the Company’s stockholders for ratification.

May 20, 2020February 21, 2023

OTHER BUSINESS

The Board of Directors knows of no other business to be presented for action at the Meeting. If any matters do come before the Meeting on which action can properly be taken, it is intended that the proxies shall vote in their discretion.

Whether or not you expect to participate in the virtual Meeting, please follow the instructions on the Notice of Internet Availability of Proxy Materials to vote via the Internet or telephone, or request, sign, date and return a proxy card so that you may be represented at the Meeting. The Meeting will be a completely virtual meeting of stockholders and will be conducted exclusively by webcast. To participate in the Meeting, visit www.virtualshareholdermeeting.com/AINV2020,MFIC2023, and, in each case, enter the16-digit control number included in your Notice of Internet Availability of Proxy Materials, on the proxy card you received, or in the instructions that accompanied your proxy materials. Onlinecheck-in will begin at 9:4530 a.m., Eastern Time. Please allow time for onlinecheck-in procedures. For questions regarding the virtual Meeting please call the support number that will be posted on the virtual meeting platformlog-in page at www.virtualshareholdermeeting.com/AINV2020.MFIC2023. For questions regarding voting, please contact us by calling us collectour proxy solicitor, Georgeson toll-free at 888-643-8150.

SUBMISSION OF STOCKHOLDER PROPOSALS

The submission of a proposal does not guarantee its inclusion in the Company’s proxy statement or presentation at an annual meeting of stockholders unless certain securities law requirements are met. A stockholder who intends to present a proposal at that Meeting pursuant to Rule14a-8 under the Exchange Act (“Rule14a-8”) must submit the proposal in writing to the Company at its address in New York, New York, and the Company must receive the proposal no later than February 22, 2021,March 12, 2024, in order for the proposal to be considered for inclusion in the Company’s proxy statement for that meeting.

Pursuant to our current bylaws, notices of business proposals or a nomination(s) of individuals for election as a director at the 20212024 Meeting, other than stockholder proposals to be included in our proxy statement pursuant to Rule14a-8, should be addressed to Joseph D. Glatt,Kristin Hester, Corporate Secretary, ApolloMidCap Financial Investment Corporation, 9 West 57th Street, New York, New York 10019 and should be received by the Company not earlier than January 23, 2021February 11, 2024 and not later than 5:00 p.m. (Eastern Time) on February 22, 2021.March 12, 2024. In the event that the date of the next annual meeting is advanced or delayed by more than 30 days from the first anniversary of the Meeting a notice by the stockholder, to be timely, must be so delivered not earlier than the 150th day prior to the date of such annual meeting and not later than 5:00 p.m. (Eastern Time), on the later of the 120th day prior to the date of such annual meeting or the tenth day following the day on which public announcement of the date of such meeting is first made. The Company reserves the right to reject, rule out of order, or take other appropriate action with respect to any proposal that does not comply with these and other applicable requirements. A stockholder’s notice must contain information specified in our bylaws about the stockholder, its affiliates, and the proposed business or nominee for election as a director.

The Company’s Audit Committee has established guidelines and procedures regarding the receipt, retention and treatment of complaints regarding accounting, internal accounting controls or auditing matters (collectively, “Accounting Matters”). Persons with complaints or concerns regarding Accounting Matters may submit their complaints to the Company’s Chief Compliance Officer (“CCO”). Persons who are uncomfortable submitting complaints to the CCO, including complaints involving the CCO, may submit complaints directly to the Company’s Audit Committee Chair. Complaints may be submitted on an anonymous basis.

The CCO may be contacted at:

ApolloMidCap Financial Investment Corporation

Chief Compliance Officer

9 West 57th Street

New York, New York 10019

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The Audit Committee Chair may be contacted at:

ApolloMidCap Financial Investment Corporation

Audit Committee Chair

9 West 57th Street

New York, New York 10019

RECEIPT OF MULTIPLE PROXY CARDS

Some of the Company’s stockholders hold their shares in more than one account and may receive a separate Notice of Internet Availability of Proxy Materials for each of those accounts. To ensure that all of your shares are represented at the Meeting, we recommend that you vote by following the instructions in each Notice of Internet Availability of Proxy Materials you receive.

FINANCIAL STATEMENTS AND OTHER INFORMATION

The Company files periodic reports, current reports, proxy statements and other information with the SEC. This information is available on the SEC’s website at www.sec.gov. This information, including the Company’s most recent AnnualTransition Report on Form10-K,10-KT, is also available free of charge by calling collect at212-515-3450, or by writing to ApolloMidCap Financial Investment Corporation, 9 West 57th Street, New York, New York 10019. Attention: Secretary or on its websitehttps://www.apolloic.com. www.midcapfinancialic.com. The information on these websites is not incorporated by reference into this proxy statement.

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        TO VOTE, MARK BLOCKS BELOW IN BLUE OR BLACK INK AS FOLLOWS:

D19000-P41661 V16836-P92606 KEEP THIS PORTION FOR YOUR RECORDS

— — — — — — — — — — — —  — — — — — — — — — — — — — — — — — — — —  — — — — — — — — — — — — — — — —

DETACH AND RETURN THIS PORTION ONLY

THIS PROXY CARD IS VALID ONLY WHEN SIGNED AND DATED.

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting: The Notice and Proxy Statement and 10-K Wrap are available at www.proxyvote.com. V16837-P92606 MIDCAP FINANCIAL INVESTMENT CORPORATION Annual Meeting of Stockholders July 10, 2023 10:00 a.m. This proxy is solicited by the Board of Directors The undersigned hereby appoints GREGORY W. HUNT and KRISTIN HESTER or either one of them, and each with full power of substitution, to act as proxies for the undersigned to vote all the shares of Common Stock of Midcap Financial Investment Corporation, a Maryland corporation (the “Company”), which the undersigned is entitled to vote at the Annual Meeting of Stockholders of the Company to be held via live webcast over the Internet at www.virtualshareholdermeeting.com/MFIC2023 on Monday, July 10, 2023 at 10:00 a.m., Eastern Daylight Time, and all postponements and adjournments thereof, as indicated on this proxy and to otherwise represent the undersigned with all powers possessed by the undersigned if personally present at the meeting. THIS PROXY IS REVOCABLE AND WILL BE VOTED AS DIRECTED, BUT IF NO INSTRUCTIONS ARE SPECIFIED, THIS PROXY WILL BE VOTED “FOR” THE NOMINEES LISTED AND “FOR” THE PROPOSAL LISTED. The validity of this proxy is governed by Maryland law. This proxy does not revoke any prior proxies except for prior proxies given in connection with the Annual Meeting. Continued and to be signed on reverse side