Born in Northern Ireland, the son of an air force pilot, Stevenson grew up in England. As a child, he developed an interest in acting when going to Saturday morning matinees. But his focus remained elsewhere, and after college he initially pursued a career as an engineer. It wasn’t until seeing a performance by John Malkovich in the play, “Burn This” at a West End theater that he decided to give acting his full attention. At age 27, he began studying acting at the Bristol Old Vic Theater School.
One of his earliest roles was in the British television drama “The Dwelling Place,” an adaptation of a popular novel by Catherine Cookson. That was followed with “Some Kind of Life,” a work for which he was later most proud, where he played a man severely injured in a motorcycle crash, with the story focusing on the grief experienced by his wife (Jane Horrocks). He appeared in a number of British television dramas from there on, including the police drama “City Central” and “Band of Gold,” where he met actress Ruth Gemmell, whom he later married. They then played husband and wife in “Peak Practice.” He also appeared in “At Home with the Braithwaites,” “Green-Eyed Monster” and “Murphy’s Law: Kiss and Tell,” among others. His first big-budget Hollywood feature was “King Arthur” (2004) where he played the part of Dagonet, alongside stars Clive Owen, Kiera Knightley and Ioan Gruffud.