[2] Gilday was born in Lowell, Massachusetts, and is a 1985 graduate of the United States Naval Academy as a surface warfare officer.

[2][6] Gilday was awarded the Navy Commendation Medal with Valor for his actions aboard Princeton when the ship was damaged by an Iraqi mine during the Persian Gulf War.

[7] On April 15, 2020, Gilday announced the Navy was considering reinstating Brett Crozier, earlier fired in relation to his controversial response to coronavirus disease on the aircraft carrier USS Theodore Roosevelt.

[11] Gilday and the acting United States Secretary of the Navy, James E. McPherson, recommended that Crozier be reinstated as captain of the Roosevelt on April 25, 2020.

[12] On August 10, 2020, Gilday was running on the Washington Navy Yard base, where he lives, when he "fell ill".