UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

OF THE SECURITIES EXCHANGE ACT OF 1934

For the month of October 2026

Commission File Number: 001-39240

GFL Environmental Inc.

(Translation of registrant’s name into English)

1759 Purdy Avenue, Suite 300

Miami Beach, Florida 33139

(Address of 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): ¨

EXPLANATORY NOTE

Exhibits 99.1 and 99.2 to this Report of Foreign Private Issuer on Form 6-K are hereby incorporated by reference into the Company’s Registration Statements on Form S-8 (File No. 333-236949) and Form F-10 (File No. 333-291669).

EXHIBIT INDEX

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.