Pronovost was with the Montreal Canadiens as a practice goaltender in the 1955–56 season when he played his first NHL game. On January 14, 1956, the Boston Bruins arrived to play in Montreal. The Bruins were without regular starter Terry Sawchuk and were unable to use their back up John Henderson because of equipment problems. The Canadiens loaned Pronovost to the Bruins for the game, and he recorded a shutout against his own team. Claude's brothers Marcel and Jean also played in the NHL.