He has been the head writer of Jimmy Kimmel Live since the shows debut in January, 2003. He occasionally appears acting in comedy bits for the show in front of camera as well.
He is the identical twin of Mark O'Donnell, the Tony-award winning writer of the Broadway musical, Hairspray.
He was born in Cleveland, and graduated with an A.B. degree from Harvard College in 1976. He also did graduate studies in American history at Columbia University and the University of North Carolina at Chapel Hill.