REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13A-16 OR 15D-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of May 2021

Commission File Number 001-39989

N/A

(Translation of Registrant’s name)

1744, William St. Suite 200

Montreal, QC, H3J1R4

Canada

(514) 937-002

(Address and telephone number of registrant’s principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

Form 20-F ¨ Form 40-F x

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ¨

Effective May 21, 2021, PyroGenesis Canada Inc.’s (the “Company”) board of directors approved the engagement of Raymond Chabot Grant Thornton LLP (the New Auditor) as its independent registered public accounting firm and dismissed KPMG LLP (the Former Auditor).

The report of the Former Auditor on the Company’s financial statements for the fiscal year ended December 31, 2020 did not contain an adverse opinion or a disclaimer of opinion and were not qualified or modified as to uncertainty, audit scope, or accounting principles.

During the fiscal year ended December 31, 2020 and the subsequent interim period through May 21, 2021 there were (i) no “disagreements” (as that term is defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions) between the Company and the Former Auditor on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedure, which disagreements, if not resolved to the satisfaction of the Former Auditor, would have caused the Former Auditor to make reference to the subject matter of the disagreement in its reports on the Company’s financial statements and (ii) no “reportable events” (as that term is defined in Item 304(a)(1)(v) of Regulation S-K and the related instructions).

During the fiscal year ended December 31, 2020 and the subsequent interim period through May 21, 2021 neither the Company, nor anyone on its behalf, consulted the New Auditor regarding (i) the application of accounting principles to a specified transaction, either completed or proposed, or the type of audit opinion that might be rendered on the Company’s combined financial statements, and neither a written report or oral advice was provided to the Company by the New Auditor that the New Auditor concluded was an important factor considered by the Company in reaching a decision as to any accounting, auditing or financial reporting issue or (ii) any matter that was the subject of a “disagreement” (as that term is defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions) or a “reportable event” (as that term is defined in Item 304(a)(1)(v) of Regulation S-K).

EXHIBIT LIST

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, thereunto duly authorized.