A product of the Gymnase Hercule de Québec, Jules Sylvain began competing in weightlifting at the national level in 1945 and made his international début at the 1950 British Empire Games, where he placed fourth in the featherweight category only five pounds behind bronze medal-winner Barry Engelbrecht of South Africa. His next major stop was the 1952 Summer Olympics, where he finished 10th in a field of 22 competitors, but his greatest success came at the 1954 British Empire and Commonwealth Games, where he took silver behind Rodney Wilkes of Trinidad and Tobago. He made another appearance at the Olympic Games in 1956, placing ninth, and was fourth in the lightweight class at the 1958 British Empire and Commonwealth Games behind bronze medalist Ben Helfgott of England. At one point, he held every British Empire record in the featherweight division. He retired shortly after his last appearance at the Commonwealth Games and took up refereeing. Most notably, he was a referee at the 1976 Summer Olympics held in Montreal, and he was involved in the sport in this capacity until shortly before his death from bone cancer in November 2016.