McGugan signed for Celtic from Eastercraigs Amateurs in April 1980. However it would be over a year later - season 1985-1986 - before he got a sustained run in the first team McGugan also played regularly the following season, but the arrival of Billy McNeill as manager in the summer of 1987 saw him drop out of the first team
In October 1987 McNeill sold McGugan to Barnsley for £55,000.
He made his first team debut at 19 years of age in a 3-2 win over Hibernian on 28 April 1984. That season McGugan made 21 league appearances for Celtic and played in both legs of their first round European Cup Winner"s Cup tie against Atlético Madrid. A highlight for McGugan that season was his goal on 1 January 1986 in a 2-0 win over Rangers at Parkhead. The season also saw McGugan win a league championship medal in dramatic fashion as Celtic crushed Street Mirren 5-0 on the last day of the season as title rivals Hearts lost 2-0 away at Dundee. McGugan spent three years in Yorkshire playing for Barnsley, including a memorable 4-0 win over Chelsea in the third round of the FA Cup in January 1989, before moving to Chesterfield in 1990.
