This Reserve Force regiment originated in Montreal, Quebec on 4 June 1880, when the 85th Battalion of Infantry was authorized to be formed. Lieutenant-Colonel Julien Brosseau, VD, was the first Commanding Officer. It was redesignated as the 85th Regiment on 8 May 1900, as Le Régiment de Maisonneuve on 29 March 1920, as the 2nd (Reserve) Battalion, Le Régiment de Maisonneuve on 7 November 1940 and finally Le Régiment de Maisonneuve on 15 December 1945.

The regiment mobilized Le Régiment de Maisonneuve, CASF, on 1 September 1939. It embarked for Great Britain on 24 August 1940. It was redesignated as the 1st Battalion, Le Régiment de Maisonneuve, CASF, on 7 November 1940. 17 On 7 July 1944, the battalion landed in France as part of the 5th Infantry Brigade, 2nd Canadian Infantry Division. It suffered heavy casualties in the Battle of the Scheldt, and was notably depleted by the time of the Battle of Walcheren Causeway. The unit recovered during the winter and was again in action during the Rhineland fighting and the final weeks of the war, taking part in the final campaigns in northern Netherlands, the Battle of Groningen, and the final attacks on German soil. The overseas battalion was disbanded on 15 December 1945.

 The regiment subsequently mobilized the 3rd Battalion, Le Régiment de Maisonneuve, CASF, on 12 May 1942. It served in Canada in a home defence role as part of the 21st Infantry Brigade, 8th Canadian Division. The 3rd Battalion was disbanded on 15 October 1943.