Dennis' stage work includes Amos Hart in "Chicago" and Bill Snibson in "Me and My Girl" in the West End. He has starred in "Skylight" at the Water Mill Theatre in Newbury, "Mr Wonderful" at the Gateway Theatre in Chester, and "Misery" at the Coliseum Theatre in Oldham. He also appeared in "Just Between Ourselves" and co-starred alongside Janet Suzman in "Cherished Disappointments in Love" at London's Soho Theatre. He co-starred with Christopher Cazenove and John Duttine in a national tour of Art and as Norman Bartholomew in Anthony Shaffer's dark comedy "Murderer" at London's Menier Chocolate Factory. He later starred in a hit season of "Neville's Island" at the Birmingham Repertory Theatre.