Tensions between Anglo and French-Canadians flared during the First World War. While both French and English were used interchangeably in both Quebec and the Canadian Parliament, a lack of Francophone regiments in the Canadian Expeditionary Force discouraged many Quebecers from enlisting. No matter the situation at home, the prowess of French-Canadian units in the C.E.F was legendary.

Brillant enlisted in late 1915 with the 189th Regiment, only later being transferred to the 22nd Battalion – the Quebec based “Van Doos”. A quiet winter of 1916 for the Van Doos ended after their participation in the attack on Vimy Ridge. A bout of trench fever took Brillant out of the line until September. When he returned to the 22nd, they found themselves in desperate combat until the end of the war.

Jean Brillant earned his Victoria Cross for his actions at Amiens on August 8th, but never lived to see it, dying of his wounds on August 10th. He is buried at Villers-Bretonneux Cemetery in France, alongside other colonial troops. Lieutenant Brillant is remembered as one of five Quebecois Victoria Cross recipients of the First World War.

For most conspicuous bravery and outstanding devotion to duty when in charge of a company which he led in attack during two days with absolute fearlessness and extraordinary ability and initiative, the extent of the advance being twelve miles. On the first day of operations shortly after the attack had begun, his company's left flank was held up by an enemy machine gun. Lt. Brillant rushed and captured the machine-gun, personally killing two of the enemy crew. Whilst doing this, he was wounded but refused to leave his command. Later on the same day, his company was held up by heavy machine-gun fire. He reconnoitred the ground personally, organised a party of two platoons and rushed straight for the machine-gun nest. Here 150 enemy and fifteen machine-guns were captured. Lt. Brillant personally killing five of the enemy, and being wounded a second time. He had this wound dressed immediately, and again refused to leave his company. Subsequently this gallant officer detected a field gun firing on his men over open sights. He immediately organised and led a "rushing" party towards the gun. After progressing about 600 yards, he was again seriously wounded. In spite of this third wound, he continued to advance for some 200 yards more, when he fell unconscious from exhaustion and loss of blood. Lt. Brillant's wonderful example throughout the day inspired his men with an enthusiasm and dash which largely contributed towards the success of the operations.