Vachon followed the usual pattern at the time of first playing for the Montreal Junior Canadiens, then moving to the Quebec Aces of the AHL. He then made the trek down to Houston to play with the Apollos of the CHL prior to joining the Montreal Canadiens, making his NHL debut in the 1966-67 season with 19 games and an impressive 11-3-4 record with a 2.48 goals against average.
During the summer of 1980, Vachon was traded to the Boston Bruins. His first season in Boston was a return to a winning record, as he went 25-19-6 in 53 games. His role was reduced during his final season to 38 games with a 19-11-6 record, his 13th winning record in 16 seasons.