Jacques Demers had his best weightlifting days in the early-to-mid 1980s, beginning with an inauspicious eighth-place at the 1980 Junior World Championships. He rose to prominence on the international scene at the 1982 Commonwealth Games, where he won a bronze medal in the middleweight division behind Stephen Pinsent of England and Tony Pignone of Australia. At the 1983 Pan American Games he was third in the snatch, second in the clean and jerk, and second overall in the division after Julio Echenique of Cuba. He slipped back to eighth at that year’s World Championships and, in November, was given a nine-month suspension by the Quebec Weightlifting Federation and a three-month suspension by the national body after being charged with importing steroids and testosterone. Nonetheless Demers was able to participate at the 1984 Summer Olympics, which doubled as that year’s World Championships, and earned a silver medal behind Karl-Heinz Radschinsky of West Germany after coming in second in both the snatch and the clean and jerk.
Demers became the gold medal favorite for the 1986 Commonwealth Games, but had his financial assistance cut off after testing positive for anabolic steroids less than two weeks prior to the tournament. He also received a two-year suspension that was lifted in 1987, after a Sports Canada tribunal agreed that his specimen had been mishandled, and was eventually selected to represent his nation at the 1988 Summer Olympics. Before he could attend, however, he tested positive for steroids once again and was removed from the team. He admitted to performance-enhancing drug use the following year, testifying at the enquiries surrounding the Ben Johnson doping scandal, and retired from active competition.
Canada