Harris has worked on Broadway in both musical and dramatic roles. He played Tobias Ragg in the 2001 concert performances of "Sweeney Todd". In 2002, he performed beside Anne Heche in "Proof". In 2003, he took the role of the Emcee in "Cabaret" alongside Deborah Gibson and Tom Bosley. As a result of his critically acclaimed performance in "Cabaret", Harris was named the top-drawing headliner in the role of the Emcee by GuestStarCasting.com, outranking fellow celebrity stars John Stamos and Alan Cumming. In 2004, he performed the dual role of the Balladeer and Lee Harvey Oswald on Broadway in the revival of Stephen Sondheim's musical "Assassins". He also sang the role of Charles (initially played by Anthony Perkins in a 1966 ABC telecast) on the Nonesuch recording of Sondheim's "Evening Primrose" and portrayed Mark Cohen in the 1997 touring company of the musical "Rent", a role he satirized on the January 10, 2009, episode of "Saturday Night Live", which he hosted.