[4][5] The youngest of nineteen children, Gagnon began composing at the age of six and according to the Canadian Encyclopedia, "He took theory lessons with Léon Destroismaisons in Ste.
Anne-de-la-Pocatière from 1952-53 and studied at the Conservatoire de musique à Montréal with Germaine Malépart (piano), Clermont Pépin (composition), and Gilberte Martin (solfège) from 1957 to 1961.
[3] In May 1976, Gagnon did four concerts in Mexico and in September of the same year, Neiges was released in New York under the title Driven Snow.
[3] In the fall of 1979, Gagnon received his first Félix, an award created by the Quebecois music industry in the instrumental category for the album Le Saint-Laurent.
[7] Gagnon also composed music for many artists, such as Diane Dufresne (Le 304), Renée Claude (Je suis une femme d'aujourd'hui, Ballade pour mes vieux jours) and Nicole Martin (Mannequin).