Mick won his first inter-county medal for Dublin in 1982 when Dublin won the All-Ireland Minor Football Championship. He went on to make his debut for the Dublin senior football team in a National Football League game against Longford in 1985. In his 1991 all star year, he was on the victorious National football league Dublin team that defeated Kildare. He won his second NFL medal with Dublin in 1993, in a hard-fought final against Donegal. The game was brought to a replay which Dublin eventually won to win their 8th title.
He also won the All-Ireland senior football championship with Dublin in 1995. The game which finished on a scoreline of 1–10 to 0–12, was against Tyrone.
In the Dublin Senior Football Championship, Deegan had a successful club career with Erin's Isle. He appeared in his first Dublin championship in 1982, the same year in which he won an all-Ireland minor medal. Ballymun Kickhams went on to win the 1982 Dublin championship. He eventually won his first Dublin championship with Erins Isle in 1993 by beating Kilmacud Crokes in the final. The next three consecutive finals resulted in losses to Kilmacud Crokes in 1994, Ballyboden St Endas in 1995 and St. Sylvester's, Malahide in 1996. He won his final championship with Erins Isle in 1997. After the 1997 win, Erins Isle went on to win the 1997 Leinster Senior Club Football Championship.
Deegan also had spells playing soccer for Tolka Rovers, and for Northern Irish club Crusaders, with whom he won the Irish Premier League title in 1995 and 1997. He played as a defender.[2][3]
