He served in the Legislative Assembly of Manitoba as a Liberal-Progressive from 1936 until the time of his death, and was a cabinet minister in the governments of John Bracken, Stuart Garson and Douglas Campbell.
He served as reeve for the Rural Municipality of Taché and was an active member of l'Association des Canadiens-Français du Manitoba and in l'Association des Commissaires d'écoles Canadiens-Français du Manitoba.
He was appointed to Bracken's cabinet on September 27, 1936, as a minister without portfolio,[1] representing the interests of Manitoba's francophone community.
Marcoux was re-elected in the 1941 provincial election,[1] defeating a Social Credit candidate by 490 votes.
After serving as a minister without portfolio for over twelve years (perhaps a Canadian record), Marcoux was promoted to Municipal Commissioner by Premier Douglas Campbell on December 14, 1948.