Farrell was born in Castleknock in Dublin, he is the son of Rita,a homemaker, and Eamon Farrell who operates a health food store and was a footballer who played for Shamrock Rovers FC. Farrell has three siblings, two sisters, Claudine and Catherine, and a brother, Eamon Óg.
Farrell was educated at St. Brigid's National School in Castleknock followed by Castleknock College and Gormanston College. In the late 1980s and early 1990s, he was a promising young football player for Dublin team, Castleknock Celtic, as a goalkeeper and dated Angie Miller. Farrell auditioned for the Read his whole biography