Born in London, Bell trained as an artist at the University of Leeds and was briefly an art teacher in Birmingham before becoming a freelance cartoonist in 1977. His comic strip Maggie's Farm appeared in the London listings magazines Time Out from 1979 and later in City Limits. In 1981 he started contributing a daily strip called If to The Guardian. Since the mid-1990s he has also been that newspaper's principal editorial cartoonist. He has won many awards for his cartooning, and won both the political and strip cartoon categories at the Cartoon Arts Trust awards in 1997.
Many collected volumes of his cartoons have been published, and he has also illustrated original books in collaboration with several different authors. He has made short animated films in collaboration with Bob Godfrey, and a radio programme about the life of 18th century caricaturist James Gillray.