Brillant volunteered for service with the 89th (Temiscouata and Rimouski) Regiment (from 1920 the Fusiliers du St-Laurent) and held the rank of lieutenant.
During the night of 27/28 May 1918, in the vicinity of Boiry-Becquerelle, Brillant was called to lead a group of volunteers to help silence an outpost defended by about 50 men.