A versatile actor, who decided to become an actor at age 34 after teaching a secondary level for several years, made his debut as a quarryman in The Field (1990). He had several small roles in major Hollywood movies based in Ireland, such as Far and Away (1992) and Into the West (1992). Memorably played historical Irish figure "Michael Collins" in The Treaty (1991) (TV). Made his breakthrough in Scottish themed Braveheart (1995), which was largely filmed in Ireland, opposite Mel Gibson. He played Gibson's right-hand man "Hamish". Since then, he has appeared in numerous major films such as Mission: Impossible II (2000), Lake Placid (1999), Turbulence (1997). He has made a name for himself taking the titular role in The General (1998), based on the life of Irish criminal "Martin Cahill", for which he won the Boston Society of Film Critics Award. He appears in director John Boorman's film The Tailor of Panama (2001) as well as Martin Scorsese's Gangs of New York (2002) and Steven Spielberg's A.I. Artificial Intelligence (2001).