Exhibit 5.1

12670 High Bluff Drive

San Diego, California 92130

Tel: +1.858.523.5400 Fax: +1.858.523.5450

www.lw.com

FIRM / AFFILIATE OFFICES

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Milan

File No. 027564-0005

August 17, 2023

Gossamer Bio, Inc.

3013 Science Park Road

San Diego, CA 92121

Re:    Registration Statement on Form S-3; 162,336,800 Shares of Common Stock, Par Value $0.0001 Per Share

To the addressees set forth above:

We have acted as special counsel to Gossamer Bio, Inc., a Delaware corporation (the “Company”), in connection with the resale from time to time by the selling securityholders named in the Registration Statement (as defined below) of up to 162,336,800 shares (the “Shares”) of the Company’s common stock, par value $0.0001 per share (the “Common Stock”). The Shares include (i) 129,869,440 shares of Common Stock issued to the selling securityholders (the “Issued Shares”)and (ii) 32,467,360 shares of Common Stock (the “Warrant Shares”) issuable upon exercise of outstanding common warrants (the “Warrants”). The Shares are included in a registration statement on Form S-3 under the Securities Act of 1933, as amended (the “Act”), filed with the U.S. Securities and Exchange Commission (the “Commission”) on August 17, 2023 (the “Registration Statement”).

This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to

August 17, 2023

Page 2

the contents of the Registration Statement or the prospectus contained therein, other than as expressly stated herein with respect to the issuance of the Shares.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters. We are opining herein as to the General Corporation Law of the State of Delaware (the “DGCL”), and we express no opinion with respect to any other laws.

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof:

1.The issuance of the Issued Shares has been duly authorized by all necessary corporate action of the Company, and the Issued Shares are validly issued, fully paid and non-assessable.

2.When the Warrant Shares shall have been duly registered on the books of the transfer agent and registrar therefor in the name or on behalf of the Warrant holders, and have been issued by the Company against payment therefor (not less than par value) in the circumstances contemplated by the Warrants, the issuance of the Warrant Shares will have been duly authorized by all necessary corporate action of the Company, and the Warrant Shares will be validly issued, fully paid and non-assessable. In rendering the foregoing opinion, we have assumed that (i) the Company will comply with all applicable notice requirements regarding uncertificated shares provided in the DGCL, (ii) the Warrants have been duly executed and delivered by the Company and, under the internal laws of the State of New York, constitute valid and legally binding obligations of the Company and (iii) upon the issuance of any of the Warrant Shares, the total number of shares of Common Stock issued and outstanding will not exceed the total number of shares of Common Stock that the Company is then authorized to issue under its amended and restated certificate of incorporation, as amended.

This opinion is for your benefit in connection with the Registration Statement and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Act. We consent to your filing this opinion as an exhibit to the Registration Statement and to the reference to our firm in the prospectus contained therein under the heading “Legal Matters.” In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.

Sincerely,

/s/ Latham & Watkins LLP