Portillo's (PTLO) S-3ASR Automatic shelf registration

Exhibit 5.1

767 Fifth Avenue

New York, NY 10153-0119

+1 212 310 8000 tel

+1 212 310 8007 fax

November 14, 2022

Portillo’s, Inc.

2001 Spring Road, Suite 400

Oak Brook, IL 60523

Ladies and Gentlemen:

We have acted as counsel to Portillo’s Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing with the Securities and Exchange Commission (the “Commission”) of the Company’s Registration Statement on Form S-3 filed on the date hereof (the “Registration Statement”), under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offer, issuance and/or sale from time to time of an indeterminate amount of (i) Class A common stock, par value $0.01 per share (the “Common Stock”); and (ii) preferred stock, par value $0.01 per share (the “Preferred Stock” and, together with the Common Stock, the “Securities”) by the Company and/or selling stockholders to be identified in one or more prospectus supplements, from time to time.

In so acting, we have examined originals or copies (certified or otherwise identified to our satisfaction) of (i) the Amended and Restated Certificate of Incorporation of the Company (the “Certificate of Incorporation”); (ii) the Amended and Restated Bylaws of the Company ; (iii) the Registration Statement, including the prospectus dated the date hereof contained within the Registration Statement; and (iv) such corporate agreements, documents and other instruments and such certificates or comparable documents of public officials and of officers and representatives of the Company and have made such inquiries of such officers and representatives, as we have deemed relevant and necessary as a basis for the opinions hereinafter set forth.

In such examination, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified, conformed or photostatic copies and the authenticity of the originals of such latter documents. As to all questions of fact material to this opinion that have not been independently established, we have relied upon certificates or comparable documents of officers and representatives of the Company.

November 14, 2022 Page 2

Based on the foregoing, and subject to the qualifications stated herein, we are of the opinion that:

1. Common Stock. Assuming (i) the Registration Statement and any amendments thereto (including any post-effective amendments) will have become effective and no stop order suspending the Registration Statement’s effectiveness will have been issued and remain in effect, in each case, at the time the Common Stock is offered or issued as contemplated by the Registration Statement; (ii) the issuance (including the execution, delivery and performance thereof) and terms of the Common Stock and the terms of the offering and sale thereof have been duly authorized; (iii) the terms of the Common Stock and its issuance and sale will have been duly established in conformity with the Certificate of Incorporation and so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding on the Company and so as to comply with any requirements or restrictions imposed by any court or governmental body having jurisdiction over the Company; (iv) the Common Stock has been issued and sold as contemplated in the Registration Statement and any prospectus supplement relating thereto, and in accordance with any applicable underwriting or purchase agreement relating thereto; and (v) the Company has received the consideration therefor, then such Common Stock will be validly issued, fully paid and nonassessable.

2. Preferred Stock. Assuming (i) the Registration Statement and any amendments thereto (including any post-effective amendments) will have become effective and no stop order suspending the Registration Statement’s effectiveness will have been issued and remain in effect, in each case, at the time the Preferred Stock is offered or issued as contemplated by the Registration Statement; (ii) the issuance (including the execution, delivery and performance thereof) and terms of the Preferred Stock and the terms of the offering and sale thereof have been duly authorized; (iii) a certificate of designations with respect to the Preferred Stock has been duly filed with the Secretary of State of the State of Delaware; (iv) the terms of the Preferred Stock and its issuance and sale will have been duly established in conformity with the Certificate of Incorporation and the applicable certificate of designations and so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding on the Company and so as to comply with any requirements or restrictions imposed by any court or governmental body having jurisdiction over the Company; (v) the Preferred Stock has been issued and sold as contemplated in the Registration Statement and any prospectus supplement relating thereto, and in accordance with any applicable underwriting or purchase agreement relating thereto; and (vi) the Company has received the consideration therefor, then such Preferred Stock (including any Preferred Stock issuable upon conversion, exercise or exchange of any Securities) will be validly issued, fully paid and nonassessable.

The opinions expressed herein are limited to the corporate laws of the State of Delaware, and we express no opinion as to the effect on the matters covered by this letter of the laws of any other jurisdiction, or, in the case of Delaware, any other laws.

We hereby consent to the use of this letter as an exhibit to the Registration Statement and to any and all references to our firm in the prospectus which is a part of the Registration Statement. In giving such consent we do not hereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission.

November 14, 2022 Page 3

Very truly yours,

/s/ Weil, Gotshal & Manges LLP