Born and raised in the tough Easterhouse section of Glasgow, Lewis has described in interviews the dichotomy of his upbringing: his parents stressed the value of education, yet he his formal studies were spotty at best. When he graduated, he lacked a sense of purpose, taking a job as a roadsweeper to earn a living. Later, Lewis found employment in the local library. Encouraged by his brother, he read voraciously and thought about pursuing a career as an actor.

Although he had pursued amateur theatrics, Lewis was 32 when he committed to showbiz, joining Robert Carlyle's newly formed Raindog Theatre. His career received a boost when he was befriended by actor-director Peter Mullan whom he met at a socialist lecture. Mullan hired Lewis for a role in the short "Close" which began filming in 1991 but took some three years to complete. By that time, both actors had appeared in "Shallow Grave" (1994). Lewis went on to act in Mullan's subsequent shorts "Good Day for the Bad Guys" (1995) and the award-winning "Fridge" (1996).

Lewis joined director Kenneth Loach's unofficial stock company lending support to his two mentors in separate films: with Carlyle, he co-starred in "Carla's Song" (1996), while he essayed a recovering alcoholic alongside Mullan in "My Name Is Joe" (1998). In between, Mullan cast him as the over-righteous, somewhat dimwitted elder sibling Thomas in "Orphans" (1997), a blistering examination of a dysfunctional family. Lewis' exceptional performance was one of the film's highlights. He went on to co-star with Max Beesley in "The Match" (1999; released on video in USA in 2001) before landing his international breakthrough part as the father of a young boy who wants to become a ballet dancer in "Billy Elliot" (2000). Lewis delivered a multi-layered turn as a man coping with grief over the death of his wife, a violent strike that threatens his livelihood and the struggles of raising two sons. The actor rounded out his banner year teaming with Irish actor Sean McGinley in "What Where", a 12-minute short film of Samuel Beckett's play, and supporting Michael Caine as a boxing coach who may or may not have been involved in a murder in "Shiner" (screened at the San Sebastian Film Festival).