[1] As a player, Dempsey was a member of the St Joseph's club, winning four Laois Senior Football Championship titles with them.
[citation needed] Dempsey was appointed manager of the Laois senior team on the night of 15 September 2008.
[2][3] Despite a poor first season, with disciplinary problems surfacing in the panel, Kildare knocking the team out of the Leinster Senior Football Championship and Down knocking the team out of the All-Ireland Senior Football Championship, Dempsey was unexpectedly retained as manager for one more year.
[citation needed] Dempsey was involved when Jack Sheedy managed Longford to promotion from Division 4 of the 2015 National Football League.
[1][6] In December 2020, he was named as manager of Dublin Senior Football Championship club Ballinteer St John's.