EXHIBIT 99.1

March 27, 2026

510 Burrard Street, 3rd Floor

Vancouver BC, V6C 3B9

www.computershare.com

To: All Canadian Securities Regulatory Authorities

Subject: FIRST MINING GOLD CORP.

Dear Sir/Madam:

We advise of the following with respect to the upcoming Meeting of Security Holders for the subject Issuer:

Meeting Type :

Annual General Meeting

Record Date for Notice of Meeting :

April 21, 2026

Record Date for Voting (if applicable) :

April 21, 2026

Beneficial Ownership Determination Date :

April 21, 2026

Meeting Date :

June 09, 2026

Meeting Location (if available) :

Issuer sending proxy related materials directly to NOBO:

Vancouver, BC

Issuer paying for delivery to OBO:

Yes

Notice and Access (NAA) Requirements:

NAA for Beneficial Holders

Yes

Beneficial Holders Stratification Criteria:

Not Applicable

NAA for Registered Holders

Yes

Registered Holders Stratification Criteria:

Not Applicable

Voting Security Details:

Description

CUSIP Number

ISIN

COMMON SHARES

320890106

CA3208901064

Sincerely,

Computershare

Agent for FIRST MINING GOLD CORP.

First Mining Gold Corp. 6-K