Osisko Files PEA Update Technical Report for Windfall Project

TORONTO, April 26, 2021 - Osisko Mining Inc. (OSK:TSX. "Osisko" or the "Corporation") is pleased to announce the filing of an independent Preliminary Economic Assessment technical report which has been prepared in accordance with National Instrument 43-101 - Standards of Disclosure for Mineral Projects, on its 100% owned Windfall gold project, located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Qu?bec.

The technical report, entitled "Preliminary Economic Assessment Update for the Windfall Project" (the "Windfall PEA") and dated April 23, 2021 (effective date of April 6, 2021), has been prepared for Osisko by BBA Inc. with the assistance of a number of specialized consultants, including Andrieux & Associates Geomechanics Consulting LP, Entech Mining Ltd., GCM Consultants, Golder Associates Ltd., and WSP Canada Inc. The Windfall PEA is available on SEDAR (www.sedar.com) under Osisko's issuer profile.

Osisko's news release dated April 7, 2021 (entitled "Osisko Mining Delivers Positive PEA Update for Windfall") summarized certain key results, assumptions and estimates contained in the Windfall PEA. The Corporation is pleased to report that there are no material differences between the key results, assumptions and estimates contained in the Windfall PEA and Osisko's news release dated April 7, 2021.

About Osisko Mining Inc.
Osisko is a mineral exploration company focused on the acquisition, exploration, and development of gold resource properties in Canada. Osisko holds a 100% interest in the high-grade Windfall gold deposit located between Val-d'Or and Chibougamau in Qu?bec and holds a 100% undivided interest in a large area of claims in the surrounding Urban Barry area and nearby Qu?villon area (over 2,700 square kilometres).

Cautionary Note Regarding Technical Information
Readers are cautioned that the Windfall PEA is preliminary in nature and includes inferred mineral resources that are too speculative geologically to have economic considerations applied to them that would enable them to be categorized as mineral reserves. There is no certainty that the results, assumptions or estimates in the Windfall PEA will be realized. Mineral resources are not mineral reserves and do not have demonstrated economic viability.

For additional information:
John Burzynski
Chief Executive Officer
Telephone (416) 363-8653