Colin Farrell was born and raised in Castleknock in the Republic of Ireland. He is the son of former football player Eamonn Farrell and nephew of Tommy Farrell, both of whom played for the Irish Football Club Shamrock Rovers in the 1960s.

It was Colin's early teenage ambition to follow in his father and uncle's footsteps, however his interest soon turned toward acting and he joined the Gaiety School of Drama in Dublin. Before completing his course, Colin landed a starring role in Dierdre Purcell's miniseries “Falling for a Dancer.” He subsequently starred in the BBC series “Ballykissangel” and in Tim Roth's directorial debut The War Zone. After The War Zone he also had a small role in Thaddeus O'Sullivan's Dublin gangster movie Ordinary Decent Criminal opposite Kevin Spacey.

Farrell's first U.S. film was Tigerland directed by Joel Schumacher, which follows the story of a handful of American soldiers who are taken to the backwoods of Louisiana in 1971 to play war games in preparation for their first tour of duty in Vietnam. He was next seen as 'Jesse James' in American Outlaws.

Farrell currently lives in Dublin.