Exhibit 5.1

250 VESEY STREET • NEW YORK, NEW YORK 10281.1047

TELEPHONE: +1.212.326.3939 • FACSIMILE: +1.212.755.7306

October 20, 2020

Calyxt, Inc.

2800 Mount Ridge Road

Roseville, MN 55113

Ladies and Gentlemen:

We have acted as counsel for Calyxt, Inc., a Delaware corporation (the “Company”), in connection with the issuance and sale of 3,750,000 shares (the “Shares”) of the Company’s common stock, par value $0.0001 per share, pursuant to the Securities Purchase Agreement, dated as of October 16, 2020 (the “Purchase Agreement”), by and among the Company and the purchasers party thereto (collectively, the “Purchasers”).

In connection with the opinion expressed herein, we have examined such documents, records and matters of law as we have deemed relevant or necessary for purposes of such opinion. Based on the foregoing, and subject to the further limitations, qualifications and assumptions set forth herein, we are of the opinion that the Shares, when issued and delivered to the Purchasers pursuant to the terms of the Purchase Agreement against payment of the consideration therefor as provided therein, will be validly issued, fully paid and non-assessable.

The opinion expressed herein is limited to the General Corporation Law of the State of Delaware, as currently in effect, and we express no opinion as to the effect of the laws of any other jurisdiction.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Current Report on Form 8-K dated the date hereof filed by the Company and incorporated by reference into the Registration Statement on Form S-3 (Registration No. 333-233231) (the “Registration Statement”), filed by the Company to effect the registration of the Shares under the Securities Act of 1933 (the “Act”) and to the reference to Jones Day under the caption “Legal Matters” in the prospectus constituting a part of such Registration Statement. In giving such consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Securities and Exchange Commission promulgated thereunder.

Very truly yours,

/s/ Jones Day

AMSTERDAM • ATLANTA • BEIJING • BOSTON • BRISBANE • BRUSSELS • CHICAGO • CLEVELAND • COLUMBUS • DALLAS • DETROITDUBAI • DÜSSELDORF • FRANKFURT • HONG KONG • HOUSTON • IRVINE • LONDON • LOS ANGELES • MADRID • MELBOURNEMEXICO CITY • MIAMI • MILAN • MINNEAPOLIS • MOSCOW • MUNICH • NEW YORK • PARIS • PERTH • PITTSBURGH • SAN DIEGOSAN FRANCISCO • SÃO PAULO • SAUDI ARABIA • SHANGHAI • SILICON VALLEY • SINGAPORE • SYDNEY • TAIPEI • TOKYO • WASHINGTON