Filed pursuant to Rule 424(b)(3)

Registration No. 333-268103

PROSPECTUS SUPPLEMENT

(To Prospectus dated November 8, 2022)

PROMIS NEUROSCIENCES INC.

Up to 1,383,755 Common Shares Underlying Units

Up to 345,939 Common Shares Underlying Warrants

This Prospectus Supplement No. 03 (this “Prospectus Supplement”) amends and supplements the Prospectus dated November 8, 2022 (the “Prospectus”) of ProMIS Neurosciences Inc. (the “Company”), which forms a part of our Registration Statement on Form S-1 (Registration No. 333-268103) (our “Registration Statement”). This Prospectus Supplement is being filed to amend and supplement the information included or incorporated by reference in the Prospectus with the information contained in this Prospectus Supplement. The Prospectus and this Prospectus Supplement relate to the resale by the selling security holders named in the Prospectus (the “Selling Shareholders”) of up to an aggregate of 1,729,694 of our common shares, no par value (“common shares”), which consists of (i) up to 1,383,755 common shares that are issuable to certain of the Selling Shareholders that are party to the Unit Purchase Agreement, dated October 11, 2022 (the “Unit Purchase Agreement”); and (ii) up to 345,939 common shares that are issuable to certain of the Selling Shareholders that are party to the Unit Purchase Agreement upon the exercise of warrants to purchase our common shares that we issued to Selling Shareholders in a private placement that closed in connection with the Unit Purchase Agreement.

This Prospectus Supplement includes information from our Report on Form 8-K filed on April 3, 2023 reporting the decision by one of the Company’s directors to not stand for re-election, with his term of service to conclude effective as of the Company’s 2023 Annual Meeting of Stockholders.

This Prospectus Supplement should be read in conjunction with the Prospectus that was previously filed, except to the extent that the information in this Prospectus Supplement updates and supersedes the information contained in the Prospectus.

Investing in our securities involves risks that are described in the “Risk Factors” section beginning on page 12 of the Prospectus.

Neither the U.S. Securities and Exchange Commission (the “SEC”), nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this Prospectus Supplement is April 3, 2023.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): March 29, 2023

PROMIS NEUROSCIENCES INC.

(Exact name of registrant as specified in its charter) 

Registrant’s telephone number, including area code: (416) 847-6898

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter)

Emerging growth company x

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

On March 29, 2023, Richard Gregory, a member of the Board of Directors (the “Board”) of ProMIS Neurosciences Inc. (the “Company”), notified the Company of his intent to not stand for re-election to the Board at the Company’s 2023 Annual Meeting of Stockholders (the “Annual Meeting”) and, as a result, his term as a director of the Company, or on any committee of the Board, will end upon the conclusion of the Annual Meeting. Mr. Gregory’s decision to resign from the Board did not result from any disagreement with the Company on any matters relating to the Company’s operations, policies or practices. The Company extends its deepest gratitude to Mr. Gregory for his distinguished service to the Board and lasting contributions to the Company.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.