The Montreal native was taken 34th overall by the hometown Montreal Canadiens in the 1988 NHL Entry Draft after a fine rookie season with Verdun Junior Canadiens of the QMJHL. He returned to junior and was a 57-goal scorer for the Trois Rivieres Draveurs in 1989-90 before debuting as a pro for the AHL's Sherbrooke Canadiens in the Calder Cup playoffs.
After scoring 44 goals for the Cincinnati Cyclones of the ECHL in 1991-92, St. Amour signed with Ottawa as they prepared for their inaugural season. He played one game for the first year club but otherwise was an AHL regular. By the mid-90s he moved on to the West Coast Hockey League and became a scoring star with the San Diego Gulls In 1996 and 1997 he notched consecutive 60-goal seasons, was a two-time first team all-star and was named WCHL MVP in 1997.
He retired in 2003.