Born in Quebec City on January 27, 1949, Justice Claude C. Gagnon studied at Académie de Québec and CÉGEP Sainte-Foy before completing an LL.L. at Université Laval in 1972.
Called to the Quebec Bar in 1974, he worked in private practice until 1981 when he became a Crown prosecutor acting for the Attorney General of Quebec. In 1985, he joined the firm Blanchard Fontaine where his practice was concentrated on criminal, disciplinary and administrative law.
Throughout his career, he taught criminal law, criminal procedure and evidence at CÉGEP François‑Xavier Garneau, Université Laval and the École du Barreau.
He was appointed to the Superior Court on July 24, 2003, and was named to the Court of Appeal on November 8, 2013.