After having worked as a production assistant and producer of television films and television series in the 1970s and early 1980s, he and Mike Leigh formed the film production company Thin Manitoba Films in 1988. In addition to his collaborations with Mike Leigh, he also produced other films. He co-produced Nick Love"s first film Goodbye Charlie Bright in 2000, and the same year he formed Potboiler Productions with producer Gail Egan (who also works closely with Mike Leigh and has been involved in the production of several of his films).Through Potboiler Productions Channing Williams produced Douglas McGrath"s Nicholas Nickleby and Fernando Meirelles" Oscar-winning The Constant Gardener.
Simon Channing Williams died aged 63, on 11 April 2009 in Cornwall, five years after being diagnosed with cancer.
Leigh paid tribute saying "His great phrase was "let"s just get on with things" and right almost to the last he was still working. He was a very extraordinary big man and he will be missed universally." Leigh dedicated his 2010 film Another Year to the memory of Simon Channing Williams.
Following Channing Williams" death, Mike Leigh started to collaborate with producer Georgina Lowe, who in 2011 took over Channing Williams" half of Thin Manitoba Films.