McGrain began his career at Celtic and was one of the "Quality Street Gang", a group of young players that emerged in the late 1960s. He progressed to the first team and went on to play 659 competitive games for Celtic between 1970 and 1987, winning seven League Championships, five Scottish Cups and two Scottish League Cups. He spent his final season of his career with Hamilton, where he helped win them promotion to the Premier Division. McGrain played in the 1974 and 1982 World Cups for Scotland. His 62 caps earned him a place in the Scotland national football team roll of honour and he was inducted to the Scottish Football Hall of Fame in 2004.