He was born in Montreal in 1776 and went on to work in the fur trade with the North West Company. He established a business in grain and hay at Rivière-du-Loup (later Louiseville in Maskinongé County), also expanding into real estate and money lending. Mayrand served in the militia as an officer during the War of 1812, becoming captain and, in 1846, major. He also held several posts as commissioner in Lower Canada. He was elected to the Legislative Assembly of Lower Canada for Saint-Maurice County in 1816. Mayrand served as a member of the Special Council which governed the province following the Lower Canada Rebellion and was named to the Legislative Council of the Province of Canada in June 1841. He resigned from the council later that same month.
