Fenwick's first regular television role was in the sitcom Watching.

He has also appeared in Inspector Morse, The Brittas Empire, Minder, On the Up, The Thin Blue Line, and Bergerac.

In 1995, Fenwick played a role in the Crimewatch File episode "Sorry Sarah".

Fenwick's film credits include Party Party, Mona Lisa, Empire State, The Raggedy Rawney, I.D., The Tichborne Claimant, Janice Beard 45 WPM, The Winslow Boy, G:MT – Greenwich Mean Time and ID2: Shadwell Army.

Fenwick married former Coronation Street actress Angela Lonsdale, but in February 2010, it was announced that the couple were to separate.