 In 1939, Gagnier moved to Trois-Rivières to assume the post of music director of the Union musicale de Trois-Rivières, a position he held for the next 11 years.During that time he also taught at the Académie de Trois-Rivières.He had previously taught at the Conservatoire de musique du Québec à Montréal and the Séminaire de Nicolet.