Newman's first speaking appearance was with Third World First (now known as People and Planet), the student political organisation. He began his comedy career as an impressionist in the late 1980s before gaining fame when he appeared alongside Baddiel, Hugh Dennis and Steve Punt (among others; this was the regular quartet, however) in the BBC radio and TV programme The Mary Whitehouse Experience (1989-92). The title was a jibe at the main campaigner for "moral decency" on television, Mary Whitehouse. He and Baddiel followed this up with their own series, Newman and Baddiel in Pieces (1993). Newman was often considered a heartthrob and could have been partly responsible for the notion that comedy was becoming the new rock 'n' roll in the early 1990s.

Newman's later solo work is marked by a clear social conscience, and anti-establishment view. He covered the anti-globalisation Seattle protests of 1999 for BBC television's Newsnight programme. He has been politically active with Reclaim the Streets, the Liverpool Dockers, Indymedia and Peoples' Global Action.

Newman co-authored The Mary Whitehouse Experience Encyclopedia in 1991. He is the author of three novels: Dependence Day (1994), Manners (1998) and The Fountain At The Center Of The World (2003). The Fountain at the Centre of the World is a novel that spans across Costa Rica, Mexico, London, and The 1999 WTO protests in Seattle. It deals primarily with the way in which people are connected through the omnipresent forces of globalism and capitalism. The process of writing the book was the subject of a BBC Two television documentary Scribbling. His later work has a very clear political element, and parallels the work of contempories such as Mark Thomas, with whom he toured in 2005. His books are sometimes linked to critical theorists in the Marxist tradition, such as Fredric Jameson. He has recently written and presented a programme entitled A History of Oil for More4, a half stand-up and half serious look at the influence of oil on the West's war policy.