Léon Bellefleur was part of the second international Cobra exhibition at Liège, Belgium, in 1951 and in 1953 he joined the AUTOMATISTE movement. He studied engraving in France at Friedlander's and Desjaubert's studios in 1954, and upon his return to Québec in 1957 developed his "facetted" painting style in which his nonfigurative compositions were built up with a spatula. Later, after his return to France in 1958, he drew close to André Breton's surrealist group.
A first retrospective of Léon Bellefleur works was organized in 1968 by the NATIONAL GALLERY OF CANADA, travelling to Ottawa, London (Ontario) and Montréal. Numerous exhibitions of his work have been held in Brazil, Canada, England and Denmark. He was, in 1977, the first winner of the Prix Borduas; he also received the annual prize of the Société Saint-Jean-Baptiste in 1985 and an honorary Ph.D. from Concordia University in 1987. Léon Bellefleur was inducted into the ROYAL CANADIAN ACADEMY in 1989.