The highlight of his time at Belfield was the 1983–84 season where he picked up an FAI Cup winners medal, scoring "after a mazy dribble" in the replay as UCD beat Shamrock Rovers 2–1.
He captained the Ireland youth team that qualified for the 1982 European Championships in Finland, but was unavailable for the finals because of university examinations.
Drawn against English club Everton in the first round, The Times' match preview picked out Hanrahan as a player to watch.
Unsettled after two years without a competitive appearance, and despite speculation about a £40,000 transfer to Port Vale,[9] Hanrahan's contract was cancelled and he returned to Ireland.
He then joined Bohemians alongside his brother Peter, a move which caused some surprise because of his age and reputation for being injury-prone, and also played for Monaghan United before retiring [14]