Son of Béloni Mazerolle and Flavie Cyr, Mathieu was born in Saint-André. He was a boarder at Hôtel-Dieu in Saint-Basile from 1912 to 1914. Mathieu studied at Caraquet College, at Sainte-Anne College in Church Point, Nova Scotia. He studied theology at the Holy Heart Seminary in Halifax and was ordained priest in Québec in 1927. Father Mazerolle was parish priest of Saint-Léonard-Parent for twenty-two years. He finally was a parish priest in Rivière-Verte where he founded a home for the old people. In 1973 he was named Honorary Prelate and retired in Rivière-Verte.