Stevens was born in Croydon, London. He was adopted at birth, by parents who were both teachers, and grew up in Wales and southeast England. He has a younger brother who was also adopted. Stevens boarded on a scholarship at Tonbridge School, an independent school in Kent. There he became interested in drama after auditioning for the title role in Macbeth with his teacher, novelist Jonathan Smith. From the age of 15, he spent his summers training and performing with the National Youth Theatre in London.\n', '
Stevens studied English Literature at Emmanuel College, Cambridge. While at Cambridge, he was a member of the Footlights with Stefan Golaszewski, Tim Key and Mark Watson, and was also active in the Marlowe Society. He was first spotted by director Peter Hall at a Marlowe Society production of Macbeth, in which he played the title character alongside Hall\'s daughter, actress Rebecca Hall.\n', '
In 2004, Stevens began his professional acting career when Peter Hall cast him as Orlando in his touring production of Shakespeare\'s As You Like It. The tour took the production to the Rose Theatre in Kingston upon Thames, the Brooklyn Academy of Music in New York City, the Curran Theatre in San Francisco, and the Ahmanson Theatre in Los Angeles. His debut performance earned him glowing reviews from prominent critics in Britain and the United States, as well as a commendation at the 2004 Ian Charleson Awards.\n', '