In 1993, Lewis won the Writers' Guild of Great Britain TV - Original Drama Series Award for Between the Lines. The award was shared with the other writers of the show at the time, J.C. Wilsher, Rob Heyland, Steve Trafford and Michael Russell.
Lewis began his career as a child actor, first appearing in the films The Looking Glass War (1969) and Sunday Bloody Sunday (1971). He played the 7-year-old Winston Churchill in Young Winston (1972), and featured in the 1973 horror films Tales That Witness Madness (as a boy who befriends an invisible tiger) and Voices. He also starred as George Gathercole in The Kids from 47A. He appeared as the young Lucius in I, Claudius (1976) and in an episode of London's Burning in 1989.
By the mid-1980s, Lewis had begun to write for television series; his writing credits include episodes of Perfect Scoundrels, Taggart, The Bill, Wycliffe, Inspector Morse, Kavanagh QC, The Ambassador, Monsignor Renard, Playing the Field, Without Motive, The Last Detective, Murphy's Law, Spooks and Lewis. Lewis has co-written three of the Sharpe films, Sharpe's Battle, Sharpe's Challenge and 2008's Sharpe's Peril. He also penned several episodes of Cadfael and an episode of Hornblower.
In 1993, Lewis won the Writers' Guild of Great Britain TV - Original Drama Series Award for Between the Lines. The award was shared with the other Writers of the show at the time, J.C. Wilsher, Rob Heyland, Steve Trafford and Michael Russell.
In 2009, Russell adapted Agatha Christie's novel The Pale Horse for the fifth series of ITV's Agatha Christie's Marple, starring Julia McKenzie, which first aired in 2010.
He devised and wrote the Inspector Morse prequel Endeavour which was first broadcast on 2 January 2012. He wrote the pilot film and all 22 of the subsequent two-hour instalments so far.