EX-5.1

Exhibit 5.1

Goodwin Procter LLP

100 Northern Avenue
Boston, MA 02210

goodwinlaw.com

+1 617 570 1000

May 16, 2024

Monte Rosa Therapeutics, Inc.

321 Harrison Avenue, Suite 900

Boston, MA 02118

Re:

Securities Registered under Registration Statement on Form S-3

We have acted as counsel to you in connection with your filing of a Registration Statement on Form S-3 (File No. 333-266003) (as amended or supplemented, the “Registration Statement”) filed on July 1, 2022 with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), relating to the registration of the offer by Monte Rosa Therapeutics, Inc., a Delaware corporation (the “Company”) of up to $300,000,000 of any combination of securities of the types specified therein. The Registration Statement was declared effective by the Commission on July 13, 2022. Reference is made to our opinion letter dated July 1, 2022 and included as Exhibit 5.1 to the Registration Statement. We are delivering this supplemental opinion letter in connection with the prospectus supplement (the “Prospectus Supplement”) filed on May 16, 2024 by the Company with the Commission pursuant to Rule 424 under the Securities Act. The Prospectus Supplement relates to the offering by the Company of up to 21,277,000 shares of the Company’s common stock, par value $0.0001 per share (“Common Stock”), consisting of (i) 10,638,476 shares of Common Stock (the “Shares”) and (ii) up to 10,638,524 shares of Common Stock issuable upon the exercise of pre-funded warrants (the “Pre-Funded Warrants”) and the shares issuable upon exercise of the Pre-Funded Warrants, (the “Pre-Funded Warrants Shares”), in each case covered by the Registration Statement. The Shares and the Pre-Funded Warrants are being sold to the several underwriters named in, and pursuant to, an underwriting agreement among the Company and such underwriters (the “Underwriting Agreement”).

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinions set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinions set forth below, on certificates of officers of the Company.

For purposes of the opinion set forth in numbered paragraph 3, we have assumed that before the Pre-Funded Warrants Shares are issued, the Company does not issue shares of Common Stock or reduce the total number of shares of Common Stock that the Company is authorized to issue under its certificate of incorporation such that the number of unissued shares of Common Stock authorized under the Company’s certificate of incorporation is less than the number of Pre-Funded Warrants Shares.

The opinions set forth below are limited to the Delaware General Corporation Law.

Based on the foregoing, we are of the opinion that:

The Shares have been duly authorized and, when delivered and paid for in accordance with the terms of the Underwriting Agreement, will be validly issued, fully paid and non-assessable.

When the Pre-Funded Warrants are delivered and paid for in accordance with the Underwriting Agreement, assuming the due authorization, execution and delivery of such Pre-Funded Warrants by the Company, the Pre-Funded Warrants will constitute valid and binding obligations of the Company.