Within six months of joining Celtic, Wallace was to attain Scottish footballing immortality, as one of the "Lisbon Lions", the famous team who won the European Cup in 1967. He was later part of the team that reached the 1970 European Cup Final but was defeated 2–1 by Feyenoord. He also won the league championship in each of the four seasons he was at the Glasgow club, plus the Scottish Cup in 1967, 1969 and 1971 and the League Cup in 1968 and 1968 during an era widely considered the greatest in the club's history. In total, he scored 140 goals for Celtic in 239 games.