Born in Greenwich, London, in 1961, he was abandoned by his father as a child and brought up by his mother. He admits that he was not particularly interested in school, except for English and Drama, and moved to a stage school.
At the age of 17, he was spotted by the director Alan Clarke, who was impressed by Sean's ability to do a Liverpool accent and cast him in his film about Borstal life, Scum (1979). He has since played tough guy roles in both British and American movies.