At age 6 Mathieu gave his first recital of his own composition at the Ritz Carlton Hotel in Montreal, Quebec, on 25 February 1935.
He remained in New York with his family until 1943, studying composition with Harold Morris and fulfilling concert and radio engagements.
In 1941 when he was not yet 12 years old, Mathieu won the first prize at the composition competition to commemorate the 100th anniversary of the New York Philharmonic Orchestra.
In 1943 he returned to Montreal and gave numerous concerts performing Bach, Beethoven, Chopin, Liszt, Debussy and Ravel, as well as his own works.
André died suddenly at the age of 39 on 2 June 1968 and was entombed at the Notre Dame des Neiges Cemetery in Montreal.
[3][7] The André-Mathieu Club was founded in 1942 at Trois-Rivières by Mme Anaïs Allard-Rousseau to promote an interest in music among youth in the community.
In October 1979 the Salle André-Mathieu opened as part of Montmorency College in Laval, Quebec, in honour of Mathieu's talent and contribution to music.
The renowned pianist and classical music activist Alain Lefèvre has popularized several of André Mathieu's works.
As a composer Mathieu's style leaned towards the late Romantic school of Rachmaninov, and his music was influenced by Debussy as well.
He also composed a fourth concerto around the year 1947, considered by some as a more mature and original work, which is currently being rediscovered and has received its first integral recording in 2008 from the Quebec music company Analekta.
Lefevre worked with conductor and composer Gilles Bellemare to reconstruct and publicize the composition, and on 10 December 2013, 70 years after the last of Mathieu's three appearances on stage at Carnegie Hall in New York City, Lefevre appeared at Carnegie Hall and gave the New York premiere of Mathieu's previously lost Piano Concerto No.4.
Mathieu's vocal works include Le ciel est si bleu, Hymne du Bloc Populaire, Les Chères Mains (1946), and Quatre Mélodies (1948).