As an actor he has starred in numerous film projects, including Stigmata, The Man in the Iron Mask opposite Leonardo DiCaprio and the compelling drama Smilla's Sense of Snow, with Julia Ormond. In addition, he earned critical acclaim for his role in The Usual Suspects. Behind the camera, Byrne executive produced the historic drama In the Name of the Father, which earned several Oscar® nominations, including Best Picture, and he co-wrote and produced Into the West, in which he also starred with Ellen Barkin.

Byrne began his acting career on the stage in Ireland, performed at the Abbey Theatre and at the Royal Court Theatre in London.

He made his feature film debut in John Boorman's epic Excalibur and went on to star in Costa-Gavra's Hanna K and the acclaimed British feature Defense of the Realm. Byrne's first American film was the Coen brothers' Miller's Crossing. He has since had starring roles in such films as Cool World, A Dangerous Woman, Trial by Jury, Point of No Return and Little Women.

His recent projects include: Polish Wedding, opposite Claire Danes; Wim Wender's The End of Violence; Frankie Starlight, opposite Matt Dillon and Anne Parillaud; and Jim Jarmusch's Dead Man, in which he starred opposite Johnny Depp.

In addition to his work in film, Byrne has recently found success as an author. His first book, Pictures in My Head, became an immediate best-seller in Ireland and received excellent reviews in the United States.