Lewis was born in Leeds, West Yorkshire, England, the son of Adrian and Lynda Lewis. He has two older brothers, Chris Lewis, a television editor, and Anthony Lewis, an actor and musician. He enjoys listening to Oasis, The Cribs, Arctic Monkeys, The Beatles & Stupid Fresh. He is a keen supporter of Leeds United. He went to St Mary's School, Menston.
Lewis has been acting since he was five years old. He started off with minor parts in television programmes, debuting in Some Kind of Life, and then went on to try out for the part of Neville Longbottom. He has portrayed Neville Longbottom in the first six Harry Potter films and is scheduled to be in the future Harry Potter films. For his role as Neville, Lewis wears yellow and crooked false teeth, two-sizes-too-big shoes and has plastic bits placed behind his ears in order to make them stick out more. This is done to give the character a more clownish look. During the filming of Harry Potter and the Order of the Phoenix, Helena Bonham Carter, who portrays Bellatrix Lestrange, accidentally ruptured Lewis's eardrum when she stuck her wand in his ear. Lewis is also known to be a fan of the books and has read them and modeled his acting on Neville. He is a great fan of 24. He is an avid cricket fan, and according to his twitter, has his own fantasy league.