EX-5.1

Exhibit 5.1

JONES DAY

250 VESEY STREET • NEW YORK, NEW YORK 10281-1047

TELEPHONE: +1.212.326.3939 • FACSIMILE: +1.212.755.7306

May 9, 2019

Calyxt, Inc.

2800 Mount Ridge Road

Roseville, MN 55113

Re: Registration Statement on Form S-8 Filed by Calyxt, Inc.

Ladies and Gentlemen:

We have acted as counsel for Calyxt, Inc., a Delaware corporation (the “Company”), in connection with the Calyxt, Inc. 2017 Omnibus Incentive Plan (the “Plan”). 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 aggregate of 2,832,445 shares (the “Shares”) of common stock, par value $0.0001 per share, of the Company that may be issued or delivered and sold pursuant to the Plan and the authorized forms of stock option, restricted stock unit or other applicable award agreements thereunder (the “Award Agreements”) will be, when issued or delivered and sold in accordance with the Plan and the Award Agreements, validly issued, fully paid and nonassessable, provided that the consideration for the Shares is at least equal to the stated par value thereof.

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 on the opinion expressed herein. In addition, we have assumed that the resolutions authorizing the Company to issue or deliver and sell the Shares pursuant to the Plan and the Award Agreements will be in full force and effect at all times at which the Shares are issued or delivered and sold by the Company, and that the Company will take no action inconsistent with such resolutions. In rendering the opinion above, we have assumed that each award under the Plan will be approved by the Board of Directors of the Company or an authorized committee of the Board of Directors.

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