Exhibit 5

ATTORNEYS AT LAW

777 EAST WISCONSIN AVENUE

MILWAUKEE, WI 53202-5306

414.271.2400 TEL

414.297.4900 FAX

WWW.FOLEY.COM

March 7, 2024

Mayville Engineering Company, Inc.

135 South 84th Street, Suite 300

Milwaukee, Wisconsin 53214

Ladies and Gentlemen:

We have acted as counsel for Mayville Engineering Company, Inc., a Wisconsin corporation (the “Company”), in connection with the preparation of a Registration Statement on Form S-3 (the “Registration Statement”), including the prospectus constituting a part thereof (the “Prospectus”), to be filed with the Securities and Exchange Commission (the “SEC”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the issuance and sale by the Company from time to time of an indeterminate amount of: (i) debt securities of the Company (the “Debt Securities”); (ii) shares of the Company’s common stock, no par value per share (the “Common Stock”); (iii) shares of the Company’s preferred stock, par value $0.01 per share (the “Preferred Stock”); (iv) warrants to purchase securities of the Company (the “Warrants”); (v) contracts to purchase shares of Common Stock or other securities of the Company (the “Purchase Contracts”); (vi) units, each comprised of a Purchase Contract and either debt obligations or other securities of the Company or debt obligations of third parties securing the holder’s obligation to purchase securities under the Purchase Contract (the “Purchase Units”); and (vii) units of the Company, each consisting of any interest in two or more securities of the types described in the Registration Statement, or a combination thereof (the “Units” and, together with the Debt Securities, the Common Stock, the Preferred Stock, the Warrants, the Purchase Contracts and the Purchase Units, the “Securities”). The Prospectus provides that it will be supplemented in the future by one or more supplements to such Prospectus and/or other type of offering document, supplement or material (each, a “Prospectus Supplement”).

As counsel to the Company in connection with the proposed issuance and sale of the Securities, we have examined: (i) the Registration Statement, including the Prospectus, and the exhibits (including those incorporated by reference) constituting a part of the Registration Statement; (ii) the Company’s Amended and Restated Articles of Incorporation and Bylaws, each as amended to date; (iii) the Form of Indenture of the Company filed as an exhibit to the Registration Statement; (iv) resolutions of the Board of Directors of the Company relating to the registration of the Securities; and (v) such other proceedings, documents and records as we have deemed necessary to enable us to render this opinion.

In our examination of the above-referenced documents, we have assumed the genuineness of all signatures, the authenticity of all documents, certificates and instruments submitted to us as originals and the conformity with the originals of all documents submitted to us as copies. We have also assumed that (i) the Registration Statement, and any amendments thereto

AUSTIN

BOSTON

CHICAGO

DALLAS

DENVER

DETROIT

HOUSTON

JACKSONVILLE

LOS ANGELES

MADISON

MEXICO CITY

MIAMI

MILWAUKEE

NEW YORK

ORLANDO

SACRAMENTO

SALT LAKE CITY

SAN DIEGO

SAN FRANCISCO

SILICON VALLEY

TALLAHASSEE

TAMPA

WASHINGTON, D.C.

BRUSSELS

TOKYO

March 7, 2024

Page 2

(including post-effective amendments), will comply with all applicable laws; (ii) a Prospectus Supplement, if required, will have been prepared and filed with the SEC describing the Securities offered thereby; (iii) all Securities will be issued and sold in compliance with applicable federal and state securities laws and in the manner stated in the Registration Statement and any applicable Prospectus Supplement; (iv) any indenture providing for the issuance of Debt Securities, together with any supplemental indenture or officer’s certificate setting forth the terms of a series of Debt Securities to be issued under such indenture, will each be duly authorized, executed and delivered by the parties thereto in substantially the form reviewed by us; (v) a Form T-1 will be filed with the SEC with respect to the trustee executing any indenture or any supplemental indenture to such indenture; (vi) a definitive purchase, underwriting, placement, dealer or similar agreement with respect to any Securities offered will have been duly authorized and validly executed and delivered by the Company and the other parties thereto; (vii) any Securities issuable upon conversion, exchange or exercise of any Security being offered will have been duly authorized, created and, if appropriate, reserved for issuance upon such conversion, exchange or exercise; and (viii) with respect to shares of Common Stock or Preferred Stock offered, there will be sufficient shares of Common Stock or Preferred Stock authorized under the Company’s Amended and Restated Articles of Incorporation, as amended, and not otherwise reserved for issuance.

Based upon and subject to the foregoing and the other matters set forth herein, and having regard for such legal considerations as we deem relevant, we are of the opinion that:

1.All requisite action necessary to make any Debt Securities valid, legal and binding obligations of the Company subject to (i) bankruptcy, insolvency, reorganization, fraudulent transfer, fraudulent conveyance, moratorium and other similar laws of general application affecting the rights and remedies of creditors and (ii) general principles of equity, regardless of whether applied in a proceeding in equity or at law, shall have been taken when:

b.The terms of such Debt Securities and of their issuance and sale shall have been established in conformity with the underlying indenture so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirements or restrictions imposed by any court or governmental entity having jurisdiction over the Company;

c.Such Debt Securities shall have been duly executed, authenticated and delivered in accordance with the terms and provisions of the underlying indenture; and

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d.Such Debt Securities shall have been issued and sold for the consideration contemplated by, and otherwise in conformity with, the Registration Statement, as supplemented by a Prospectus Supplement with respect to such issuance and sale, and the acts, proceedings and documents referred to above.

2.All requisite action necessary to make any shares of Common Stock validly issued, fully paid and nonassessable will have been taken when:

a.The Company’s Board of Directors, or a committee thereof duly authorized by the Board of Directors, shall have adopted appropriate resolutions to authorize the issuance and sale of such shares of Common Stock; and

b.Such shares of Common Stock shall have been issued and sold for the consideration contemplated by, and otherwise in conformity with, the Registration Statement, as supplemented by a Prospectus Supplement with respect to such issuance and sale, and the acts, proceedings and documents referred to above.

3.All requisite action necessary to make any shares of Preferred Stock validly issued, fully paid and nonassessable will have been taken when:

a.The Company’s Board of Directors, or a committee thereof duly authorized by the Board of Directors, shall have adopted appropriate resolutions to establish the powers, designations, preferences and relative, participating, optional or other rights, if any, or the qualifications, limitations or restrictions, if any, and other terms of such shares as set forth in or contemplated by the Registration Statement, the exhibits thereto and any Prospectus Supplement relating to the Preferred Stock, and to authorize the issuance and sale of such shares of Preferred Stock;

b.Articles of Amendment to the Company’s Amended and Restated Articles of Incorporation, as amended, with respect to the powers, designations, preferences and relative, participating, optional or other rights, if any, or the qualifications, limitations or restrictions, if any, and other terms of such shares shall have been filed with the Department of Financial Institutions of the State of Wisconsin in the form and manner required by law; and

c.Such shares of Preferred Stock shall have been issued and sold for the consideration contemplated by, and otherwise in conformity with, the Registration Statement, as supplemented by a Prospectus Supplement with respect to such issuance and sale, and the acts, proceedings and documents referred to above.

4.All requisite action necessary to make any Warrants valid, legal and binding obligations of the Company, subject to (i) bankruptcy, insolvency, reorganization, fraudulent

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transfer, fraudulent conveyance, moratorium and other similar laws of general application affecting the rights and remedies of creditors and (ii) general principles of equity, regardless of whether applied in a proceeding in equity or at law, shall have been taken when:

a.The Company’s Board of Directors, or a committee thereof or one or more officers of the Company, in each case duly authorized by the Board of Directors, shall have taken action to approve and establish the terms and form of the Warrants and the documents, including any warrant agreements, evidencing and used in connection with the issuance and sale of the Warrants, and to authorize the issuance and sale of such Warrants;

b.The terms of such Warrants and of their issuance and sale shall have been established so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirements or restrictions imposed by any court or governmental entity having jurisdiction over the Company;

c.Any such warrant agreements shall have been duly executed and delivered;

d.Such Warrants shall have been duly executed and delivered in accordance with the terms and provisions of the applicable warrant agreement; and

e.Such Warrants shall have been issued and sold for the consideration contemplated by, and otherwise in conformity with, the Registration Statement, as supplemented by a Prospectus Supplement with respect to such issuance and sale, and the acts, proceedings and documents referred to above.

5.All requisite action necessary to make any Purchase Contracts and Purchase Units valid, legal and binding obligations of the Company, subject to (i) bankruptcy, insolvency, reorganization, fraudulent transfer, fraudulent conveyance, moratorium and other similar laws of general application affecting the rights and remedies of creditors and (ii) general principles of equity, regardless of whether applied in a proceeding in equity or at law, shall have been taken when:

a.The Company’s Board of Directors, or a committee thereof or one or more officers of the Company, in each case duly authorized by the Board of Directors, shall have taken action to approve and establish the terms of the Purchase Contracts and the documents evidencing and used in connection with the issuance and sale of the Purchase Units, and to authorize the issuance and sale of such Purchase Contracts and Purchase Units;

b.The terms of such Purchase Contracts and Purchase Units and of their issuance and sale shall have been established so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and

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so as to comply with any requirements or restrictions imposed by any court or governmental entity having jurisdiction over the Company;

c.Such Purchase Contracts and Purchase Units shall have been duly executed and delivered in accordance with their respective terms and provisions; and

d.Such Purchase Contracts and Purchase Units shall have been issued and sold for the consideration contemplated by, and otherwise in conformity with, the Registration Statement, as supplemented by a Prospectus Supplement with respect to such issuance and sale, and the acts, proceedings and documents referred to above.

6.All requisite action necessary to make any Units valid, legal and binding obligations of the Company, subject to (i) bankruptcy, insolvency, reorganization, fraudulent transfer, fraudulent conveyance, moratorium and other similar laws of general application affecting the rights and remedies of creditors and (ii) general principles of equity, regardless of whether applied in a proceeding in equity or at law, shall have been taken when:

a.The Company’s Board of Directors, or a committee thereof or one or more officers of the Company, in each case duly authorized by the Board of Directors, shall have taken action to approve and establish the terms and form of such Units and the documents, including any unit agreements, evidencing and used in connection with the issuance and sale of the Units, and to authorize the issuance and sale of such Units;

b.The terms of such Units and of their issuance and sale shall have been established so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirements or restrictions imposed by any court or governmental entity having jurisdiction over the Company;

c.Such Units shall have been duly executed and delivered in accordance with the terms and provisions of the applicable unit agreement; and

d.Such Units shall have been issued and sold for the consideration contemplated by, and otherwise in conformity with, the Registration Statement, as supplemented by a Prospectus Supplement with respect to such issuance and sale, and the acts, proceedings and documents referred to above.

We express no opinion as to the laws of any jurisdiction other than the States of Wisconsin and New York and the federal laws of the United States.

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We hereby consent to the reference to our firm under the caption “Legal Matters” in the Prospectus which is filed as part of the Registration Statement, and to the filing of this opinion as an exhibit to the Registration Statement. In giving this consent, we do not admit that we are “experts” within the meaning of Section 11 of the Securities Act or within the category of persons whose consent is required by Section 7 of the Securities Act.


	Very truly yours,

	/s/Foley & Lardner LLP

	Foley & Lardner LLP