INTRODUCTION

This proxy statement (the“Proxy Statement”) is being furnished to you in connection with the solicitation of proxies by the Board of Trustees (the“Board” or“Board of Trustees”) of Pacific Funds Series Trust (the“Trust”) on behalf of all of its series (the“Funds”) to be voted at a special meeting (the“Meeting”) of shareholders of the Trust to be held on June 17, 2019. This Proxy Statement is first being mailed to shareholders on or about April 29, 2019.

PLEASE read this entire Proxy Statement carefully, including the Appendices.

PROPOSAL – ELECTION OF THREE TRUSTEES TO THE BOARD OF TRUSTEES

Which shareholders are voting on this proposal?

Shareholders of all Funds.

What are shareholders being asked to approve?

Shareholders are being asked to elect three Trustees to the Board of Trustees of the Trust: (i) James T. Morris, (ii) Paul A. Keller and (iii) Andrew J. Iseman (the“Nominees”).

Mr. Morris and Mr. Keller currently serve as Trustees of the Trust. Mr. Iseman has been nominated but does not yet serve as a Trustee of the Trust. If shareholders approve the proposal, the elections would be effective June 18, 2019.

Why are shareholders being asked to elect the three Trustees?

The Board currently has five Trustees:  James T. Morris,  Gale K. Caruso, Paul A. Keller, Lucie H. Moore and Nooruddin (Rudy) Veerjee.  Three of the five Trustees have been elected by shareholders (Ms. Moore in 2001 and Mr. Veerjee and Ms. Caruso in 2005, effective in 2006).  Messrs. Morris and Keller were appointed by the Board (Mr. Morris in 2007 and Mr. Keller in 2016) to fill vacancies on the Board, but have not been elected by shareholders.  At the Board’s December 12, 2018 meeting, the Board nominated Mr. Iseman to serve as a Trustee, effective upon his election by shareholders, and he has consented to serve as a Trustee upon his election. Mr. Iseman, if elected by shareholders, would also fill an existing vacancy on the Board.

Under the Investment Company Act of 1940, as amended (the“1940 Act”), a vacancy on a mutual fund board may be filled without shareholder approval only if, upon filling the vacancy, at least two-thirds of the board members have been approved by shareholders.

Mr. Iseman cannot begin to serve as a Trustee until his appointment is approved by shareholders because, without such approval, only three of the six Trustees (less than the two-thirds requirement) would have been elected by shareholders.  Accordingly, shareholders are being asked to elect Mr. Iseman. 

Also at the Board’s December 12, 2018 meeting, Messrs. Morris and Keller were asked to stand for election so that all of the members of the Board will have been elected by shareholders, and they consented to continue to serve if elected.  Although they already serve on the Board, having Messrs. Morris and Keller be elected by shareholders is important because it will give the Board more flexibility to appoint a limited number of additional new Trustees if necessary without incurring the high costs of holding shareholder meetings to elect new Trustees.  Accordingly, shareholders are also being asked to elect Messrs. Morris and Keller.

What is the Board structure and what are the qualifications of the Trustees and Nominees?

Four of the five current Trustees are Independent Trustees, meaning they are not “interested persons” of the Trust as defined in the 1940 Act. Mr. Morris is a Management Trustee, meaning he is an “interested person” of the Trust due to his position as Chairman, Chief Executive Officer (“CEO”) and President of Pacific Life Insurance Company (“Pacific Life”), which is the parent of the Trust’s investment adviser, Pacific Life Fund Advisors LLC (the“Adviser” or“PLFA”). At the Board’s January 11, 2007 meeting, during which it was noted that the Board’s Policy Committee had discussed succession to the Chairmanship of the Board and the relationship of the Chairman with Pacific Life’s management personnel, the Board of Trustees voted unanimously to appoint Mr. Morris to serve as Chairman of the Board of Trustees, (the “Board”Chief Executive Officer and Trustee of the Trust.

The Trust’s Governance Committee, which consists solely of Independent Trustees, engaged in an extensive and deliberative process to identify and evaluate potential candidates to serve as an Independent Trustee of the Trust. After carefully reviewing and considering the qualifications, experience and background of potential candidates, which included conducting interviews with certain candidates, the Governance Committee determined at its September 16, 2015 meeting to recommend the appointment of Mr. Keller as a Trustee of the Trust. At the Board’s September 17, 2015 meeting, based upon the Governance Committee’s recommendation and additional discussion, the Board of Trustees voted unanimously to appoint Mr. Keller to serve as a Trustee of the Trust. After carefully reviewing and considering the qualifications, experience and background of potential candidates, which included conducting interviews with certain candidates, the Governance Committee determined at its September 25, 2018 meeting to recommend the nomination of Mr. Iseman as a Trustee of the Trust. At the Board’s December 12, 2018 meeting, based upon the Governance Committee’s recommendation and additional discussion, the Board of Trustees voted unanimously to nominate Mr. Iseman to serve as a Trustee of the Trust, subject to election by shareholders. In evaluating candidates, the Governance Committee takes into account all factors it considers relevant, including without limitation, experience, demonstrated capabilities, independence, commitment, reputation, background, diversity, understanding of the investment business and understanding of business, legal and financial matters generally. A copy of the Trust’s Governance Committee Charter, which includes additional factors that may be considered by the Governance Committee members when evaluating potential candidates, is set forth inExhibit A.

Term of Office for Trustees

Once duly appointed or elected, Trustees serve for an indefinite term until their retirement, resignation, removal, or death, or until their successor is duly elected. The Trust’s Governance Committee has adopted an Independent Trustee retirement policy that fixes a mandatory retirement date for the Independent Trustees of December 31 of the year in which the Independent Trustee reaches the age of 74.

Professional Background of Trustees and Nominees

The Governance Committee conducts a “self-assessment” annually to review the effectiveness of the Board and its committees. In conducting its annual self-assessment at its September 25, 2018 meeting, the Governance Committee determined that the current Trustees have the appropriate attributes and experience to continue to serve effectively as Trustees of the Trust. The Board believes that each of the current Trustees and Nominees has the qualifications, experience, attributes and skills (“Trustee Attributes”) appropriate for service as a Trustee in light of the Trust’s business and structure. Each has a demonstrated record of business and/or professional accomplishment.

The following table shows information about the three Nominees who are standing for election at the Meeting, as well as the Trustees who are not standing for election at this time, but are expected to remain on the Board following the Meeting.

Management Trustee and Nominee

Independent Trustees and Nominees

Additional Qualifications of Trustees and Nominees

In addition to the information provided in the table above, certain additional information regarding the Trustees and Nominees is provided below. The information is not all-inclusive. Many Trustee Attributes involve intangible elements, such as intelligence, integrity and work ethic, along with the ability to work together, to communicate effectively, to exercise judgment and ask incisive questions, and commitment to shareholder interests.

Ms. Caruso, Independent Trustee, has executive experience from her former positions as President and Chief Executive Officer of Zurich Life, Chairman, President and Chief Executive Officer of Scudder Canada Investor Services, Ltd. and Managing Director of Scudder Kemper Investments. Ms. Caruso also has prior insurance company board experience, having previously served as a director of LandAmerica Financial Group, Inc. (an insurance company) and on the board of directors of the Illinois Life Insurance Council as well as prior insurance fund and mutual fund board experience. Ms. Caruso also serves as a trustee of the Matthews Asia Funds (a series of mutual funds).

Ms. Moore, Independent Trustee, has significant legal experience as a former Partner with the law firm of Gibson, Dunn & Crutcher.

Mr. Veerjee, Independent Trustee, has insurance company executive experience as former President of Transamerica Insurance and Investment Group. He also has executive mutual fund and asset management experience as former President of Transamerica Asset Management and as former Chairman and Chief Executive Officer of Transamerica Premier Funds.

Mr. Keller, Independent Trustee, Nominee (standing for election), has financial accounting experience as a Certified Public Accountant and was a former Audit Partner at PricewaterhouseCoopers LLP with over 30 years of experience in the mutual fund industry. Mr. Keller also serves as a trustee of the FAM Funds (a series of mutual funds).

Mr. Iseman, Nominee (standing for election), has significant investment management and executive experience from his former positions as Chief Executive Officer of Scout Investments and President of Scout Funds (a series of mutual funds now known as the Carillon Series Trust).  Mr. Iseman also has prior investment company board experience, having previously served as an interested trustee for the Scout Funds and as a consultant for Pacific Funds Series Trust.

Mr. Morris, Management Trustee, Nominee (standing for election), is Chairman, CEO and President of Pacific Life, Funds (the “Trust”) for use at a special meeting of shareholderswhich makes him an “Interested Person” of the following funds:

Contact Information

The contact information for each Trustee and Nominee is c/o Pacific Funds Series Trust, 700 Newport Center Drive, Newport Beach, CA 92660.

Executive Officers

The business and affairs of the Trust are managed under the direction of the Board under the Trust’s Agreement and Declaration of Trust (the“Declaration of Trust”). Trust officers are appointed by the Board to oversee the day-to-day activities of each Fund. Information about the officers is set forth inExhibit B.

Leadership Structure and Committees

The Role of the Board. The Board oversees the management and operations of the Trust. Like most mutual funds, the day-to-day management and operation of the Trust is performed by various service providers to the Trust, such as the Adviser, Fund sub-advisers, the distributor, administrator, custodian, and transfer agent. The Board has appointed senior employees of certain of these service providers as officers of the Trust, with responsibility to monitor and report to the Board on the Trust’s operations. The Board receives regular reports from these officers and service providers regarding the Trust’s operations. For example, the Treasurer provides reports as to financial reporting matters and investment personnel report on the performance of the Funds. The Board has appointed a Trust Chief Compliance Officer who administers the Trust’s compliance program and regularly reports to the Board as to compliance matters. Some of these reports are provided as part of formal Board meetings which are typically held quarterly, in person, and involve the Board’s review of recent Trust operations. From time to time, one or more Independent Trustees may also meet with management in less formal settings, between scheduled Board meetings, to discuss various topics. In all cases, however, the role of the Board and of any individual Trustee is one of oversight and not of management of the day-to-day affairs of the Trust and its oversight role does not make the Board a guarantor of the Trust’s investments, operations or activities.

Board Structure, Leadership. The Board has structured itself in a manner that it believes allows it to perform its oversight function effectively. It has established four standing committees, an Audit Committee, a Policy Committee, a Governance Committee and a Trustee Valuation Committee, which are discussed in greater detail under“Committees” below. More than 75% of the members of the Board are Independent Trustees and each of the Audit, Policy and Governance Committees is comprised entirely of Independent Trustees. The Chairman of the Board is the Chairman, CEO and President of Pacific Life. The Board has a Lead Independent Trustee, who acts as the primary liaison between the Independent Trustees and management. The Independent Trustees, including the Lead Independent Trustee, help identify matters for consideration by the Board and the Lead Independent Trustee regularly participates in the agenda setting process for Board meetings. The Lead Independent Trustee serves as Chairman of the Trust’s Policy Committee, which provides a forum for the Independent Trustees to meet in separate session to deliberate on matters relevant to the Trust. The Independent Trustees have also engaged their own independent counsel to advise them on matters relating to their responsibilities in connection with the Trust. The Board reviews its structure annually. In developing its structure, the Board has considered that the Chairman of the Board, as the Chairman, CEO and President of Pacific Life, can provide valuable input as to, among other things, the operation of the Adviser and Pacific Life, their financial condition and business plans relating to the Trust. The Board has also determined that the structure of the Lead Independent Trustee and the function and composition of the Policy, Audit, Governance and Trustee Valuation Committees are appropriate means to provide effective oversight on behalf of the Trust’s shareholders and address any potential conflicts of interest that may arise from the Chairman’s status as an Interested Trustee. The Board met four times during the Funds’ fiscal year ended March 31, 2019. Each of the Trustees attended all meetings of the Board during the fiscal year ended March 31, 2019, and all of the Independent Trustees attended all meetings of the Board, Policy Committee, Audit Committee and Governance Committee held during the fiscal year ended March 31, 2019.

Board Oversight of Risk Management. As part of its oversight function, the Board receives and reviews various risk management reports and assessments and discusses these matters with appropriate management and other personnel. The full Board receives reports from PLFA and Fund sub-advisers as to investment risks as well as other risks that may be also discussed in Policy or Audit Committee. In addition, the Board receives reports from the Adviser’s Risk Oversight Committee regarding its assessments of potential material risks associated with the Trust and the manner in which those risks are addressed. Because risk management is a broad concept comprised of many elements, Board oversight of different types of risks is handled in different ways. For example, the Board and its committees periodically receive reports from Pacific Life and its Chief Risk Officer as to Pacific Life’s enterprise risk management. The Board and its committees also receive periodic reports as to how PLFA conducts service provider oversight and how it monitors for other risks, such as derivatives risk, business continuity risks and risks that might be present with individual Fund sub-advisers or specific investment strategies. The Audit Committee meets regularly with the Chief Compliance Officer to discuss compliance and operational risks. The Audit Committee also meets regularly with the Treasurer, and the Trust’s independent registered public accounting firm and, when appropriate, with other Pacific Life personnel to discuss, among other things, the internal control structure of the Trust’s financial reporting function.

Committees. As noted above, the standing committees of the Board are the Audit Committee, the Policy Committee, the Governance Committee and the Trustee Valuation Committee.

Audit Committee.The members of the Audit Committee include each Independent Trustee of the Trust. The Audit Committee operates pursuant to a separate charter and is responsible for, among other things, reviewing and recommending to the Board the selection of the Trust’s independent registered public accounting firm, reviewing the scope of the proposed audits of the Trust, reviewing with the independent registered public accounting firm the accounting and financial controls of the Trust and the results of the annual audits of the Trust’s financial statements, interacting with the Trust’s independent registered public accounting firm on behalf of the full Board, assisting the Board in its oversight of the Trust’s compliance with legal and regulatory requirements, and receiving reports from the Chief Compliance Officer. Mr. Keller serves as Chairman of the Audit Committee. The Audit Committee met four times during the fiscal year ended March 31, 2019.

Pursuant to its charter, the Audit Committee also serves as the Qualified Legal Compliance Committee for the Trust for purposes of Section 307 of the Sarbanes Oxley Act (“SOX”), regarding standards of professional conduct for attorneys appearing and practicing before the U.S. Securities and Exchange Commission on behalf of an issuer (“Reporting Attorney”). A Reporting Attorney who becomes aware of evidence of a material violation by the Trust, or by any officer, director, employee, or agent of the Trust, may report the matter to the Qualified Legal Compliance Committee as an alternative to the reporting requirements of SOX (which requires reporting to the chief legal officer and potentially “up the ladder” to other entities). The Qualified Legal Compliance Committee must take appropriate steps to respond to any reports received from a Reporting Attorney. The Qualified Legal Compliance Committee meets as necessary during the year. The Qualified Legal Compliance Committee did not meet during the fiscal year ended March 31, 2019.

Policy Committee.The members of the Policy Committee include each Independent Trustee of the Trust. The Policy Committee operates pursuant to a separate charter and its primary responsibility is to provide a forum for its members to meet and deliberate on certain matters to be presented to the Board for its review and/or consideration for approval at 9 a.m. Pacific time onBoard meetings. Mr. Veerjee serves as Chairman of the Policy Committee. The Policy Committee met five times during the fiscal year ended March 25, 2008 (the “Meeting”)31, 2019.

Governance Committee.The members of the Governance Committee include each Independent Trustee of the Trust. The Governance Committee operates pursuant to a separate charter and is responsible for, among other things, the Trustees’ “self-assessment,” making recommendations to the Board concerning the size and composition of the Board, determining compensation of the Independent Trustees, establishing an Independent Trustee retirement policy and the screening and nomination of new candidates to serve as Trustees.

With respect to new Trustee candidates, the Governance Committee may seek candidate referrals from a variety of sources and may engage a search firm to assist it in identifying or evaluating potential candidates. The Governance Committee will consider any candidate for Trustee recommended by a current shareholder if such recommendation contains sufficient background information concerning the candidate to enable the Governance Committee to make an informed judgment as to the candidate’s qualifications. The recommendation must be submitted in writing and addressed to the Governance Committee Chairperson at the offices ofTrust’s offices: Pacific Funds’ Governance Committee, c/o Pacific Life Fund Advisors LLC, (“PLFA”), located at 700 Newport Center Drive, Newport Beach, CA 92660, and at any adjournmentAttention: Governance Committee Chairperson. Ms. Moore serves as Chairperson of the Meeting, for the purposes set forth in the accompanying Notice of Special Meeting of Shareholders (“Notice”). This proxy statement will be first mailed to shareholders of the Portfolio Optimization Funds (“Shareholders”) on or about February 4, 2008.Governance Committee. The primary purpose of the Meeting is for Shareholders to consider and approve the following proposals to be effective on or about July 1, 2008:

Trustee Valuation Committee.The members of the Trustee Valuation Committee consist of any two or more Trustees, at least one of whom is an Independent Trustee of the Trust. The two or more Trustees who serve as the members may vary from meeting to meeting. The Trustee Valuation Committee’s primary responsibility is to oversee the implementation of the Trust’s valuation procedures, including valuing securities for which market prices or quotations are not readily available or are deemed to be unreliable, and (2)to review fair value determinations made by PLFA or a Fund sub-adviser on behalf of the aggregate amount of advisory fees that would have been paid toBoard, as specified in the Adviser forTrust’s valuation procedures adopted by the Board. The Trustee Valuation Committee met one time during the fiscal year ended March 31, 2007 if2019.

Beneficial Interest of Trustees and Nominees in the Amended Agreement had beenFunds

The table below shows the dollar range of equity securities beneficially owned by each Trustee or Nominee as of December 31, 2018 (unless otherwise noted) (i) in effect for that year.

As of each share class of each Portfolio Optimization Fund assuming implementationApril 5, 2019, for all Funds that have commenced operations, to the best of the new 0.20% annual advisory feeTrust’s knowledge, the Trustees, Nominees and (a) a 0.20% decrease in the annual advisory feeOfficers of the Underlying Funds; (b)Trust as a 0.05% decrease in the annual administration fee; (c) an extension of contractual expense caps through June 30, 2009; and (d) an additional 0.20% decrease in the annual advisory fee for the PL Small-Cap Growth Fund. Fees and expenses are based on average daily net assets of the applicable Fund. Appendix B also includes examples of the costs of investing in the share classes of the Portfolio Optimization Funds under these scenarios.

Compensation

The following table shows the Board closure, merger, or a change in management firm or strategy of an Underlying Fund, all of which could impact a Portfolio Optimization Fund.

VOTING REQUIREMENTS

Who has a right to vote on the Proposal?

Shareholders of record at the close of business on April 5, 2019 (the “Record Date”) are entitled to vote on the proposal.

What is the required vote?

This is a Trust-wide vote, meaning that shareholders of all Funds are voting collectively on the proposal. To be elected, provided a quorum is present, each individual standing for election must receive a plurality of the votes cast at the Meeting, meaning the three individuals who receive the most votes across all of the Funds an extension of contractual expense caps through June 30, 2009 for the Funds and an additional 0.20% decrease in the annual advisory fee that is appliedwill be elected to the average daily net assetsBoard. If as expected, no one else stands for the PL Small-Cap Growth Fund. The Board further considered the proposed advisory fee, and the changes to the Trust’s fee structure, in connection with the re-evaluation and re-positioning of the Portfolio

How can Shareholders vote on the Proposal?

Shareholders may vote by mail, telephone, Internet or in person. Voting instructions must be received by 6 a.m. Eastern time on June 17, 2019. If you vote by mail, the voting instruction proxy card must be received at the address shown on the enclosed postage paid envelope.

Shareholders may also vote by attending the Meeting in person. To attend the Meeting in person, you will be required to provide proof of ownership of an advisory fee for any Portfolio Optimization Fund and no corresponding decreaseinterest in the advisory feesFund(s) and a valid form of the Underlying Funds; and there may notidentification, such as a driver’s license, passport or other government-issued ID.

How will votes be a decrease in the Administration Fee, an extension of the contractual expense caps through June 30, 2009 and an additional decrease in the advisory fee for the PL Small-Cap Growth Fund.

Shares represented by Shareholders of each Portfolio Optimization Fund, this proposal will take effect onproperly executed proxies, unless revoked before or about July 1, 2008.

Funds of Funds of the Trust, as shareholders of underlying Funds, will vote their proxies for underlying Fund sharesin the same proportion as the votes cast on the proposal beforeby the Meeting. Shares representedshareholders of the Funds of Funds. For example, Pacific Funds Portfolio Optimization Conservative will vote its shares of the PF Inflation Managed Fund in the same proportion as the votes cast on the proposal by timelythe shareholders of Pacific Funds Portfolio Optimization Conservative. Similarly, Pacific Funds Portfolio Optimization Conservative will vote its shares of Pacific Funds Core Income, another underlying Fund, in the same proportion as the votes cast on the proposal by the shareholders of Pacific Funds Portfolio Optimization Conservative.

Broker-dealer firms holding shares in “street name” for the benefit of their customers will request the instructions of such customers on how to vote their shares on the proposal. Pursuant to the rules and policies of the New York Stock Exchange (“NYSE”), broker-dealers that are members of the NYSE that have not received instructions from their customers (or “broker non-votes”) may vote on the proposal without instructions from beneficial owners of the Trust’s shares.Broker non-votes will be excluded from any vote to adjourn the Meeting and, accordingly, will not affect the outcome of an adjournment vote.

A properly executed voting instructions willproxy card or other authorization by a customer that does not specify how the shares should be voted as specified. Executed voting instructions that are unmarked willon the proposal may also be voted in favor of the proposals set forthproposal. In this context, voting in favor of the Notice.

How will “Withhold” votes be treated?

“Withhold” votes will be counted as present for purposes of determining whether a quorum is present at the Meeting, and assuming a quorum is present, will have no effect on the proposal.

How can a vote be changed?

A proxy may be revoked at any time prior to its exercise by written notice, by execution of a subsequent proxy, or by attending the Meeting and voting in person. However, attendance at the Meeting, by itself, will not serve to revoke a proxy. An abstention (marking “Abstain”)

What is quorum?

A quorum must be present at the Meeting for action to be taken on Proposal 1 or any proposalthe proposal. Except as otherwise provided by a Shareholder will be counted for purposeslaw, the holders of establishing a quorum, and has the same effect as a negative vote (i.e. “against”) with respect to Proposal 1. Broker non-votes (i.e. proxies from brokers or nominees indicating that such persons have not received instructions from the beneficial owner or other person entitled to vote shares on a particular matter with respect to which the brokers or nominees do not have discretionary voting power) will be treated the same as abstentions. Pursuant to the rules and policies33 1/3% (or one third) of the New York Stock Exchange (“NYSE”), membersoutstanding shares of the NYSE may not vote on Proposal 1 without instructions from beneficial owners.

How can the Meeting and entitled to vote. In the absence of a quorum, the persons named as proxies will vote all shares represented by proxy and entitled to vote (including abstentions) in favor of adjournment with respect to a proposal. Ifbe postponed or adjourned?

The Meeting may be adjourned (whether or not a quorum is present with respectpresent) by a majority of the votes properly cast upon the question of adjourning the Meeting. In addition, the Meeting may be postponed or adjourned (whether or not a quorum is present) by the Trustees or the chairperson of the Meeting. The Meeting may be postponed or adjourned for up to 6 months from the original date, and may be moved to a proposal but insufficient votes to approve that proposal have been received, the persons named as proxies will vote in favor of such adjournment with respect to the proposal those proxies which they are entitled to vote in favor of the proposal and will vote against any such adjournment with respect to the proposal those proxies required to be voted against the proposal. Abstentions will not be voted either for or against the adjournment in this case. Broker non-votes will be excluded from any vote to adjourn the Meeting and, accordingly, will not affect the outcome of the vote.different location. At any subsequent reconvening of thepostponed or adjourned Meeting, proxies will (unless previously revoked) will be voted in the same manner as they would have been voted at the Meeting.

How will proxies be solicited?

The principal solicitation will be by mail, but voting instructions also may vote by written ballot,be solicited by telephone, Internet or online by followingin person. Arrangements will be made with brokerage houses and other custodian nominees and fiduciaries to forward proxy materials to shareholders.

GENERAL INFORMATION

Who is bearing the instructions oncosts associated with the Voting Instructions form accompanyingMeeting?

Costs associated with the Meeting, including the preparation and mailing of this Proxy Statement.