Matthew Robert Smith was born on 28 October 1982 in Northampton, Northamptonshire, where he was raised. He is the son of David and Lynne Smith. He has a sister named Laura Jayne, who was one of the dancers featured in the music video for Eric Prydz's song "Call on Me" (2004).
Smith attended Northampton School for Boys. His grandfather had played professionally for Notts County F.C., and Smith had planned to be a professional player, having played for the youth teams of Northampton Town, Nottingham Forest, and Leicester City, becoming captain of the latter's youth team.
A serious back injury, resulting in spondylosis, meant that he was unable to continue with a footballing career. His drama teacher introduced him to acting by signing him up for theatrical productions without his consent. After failing to participate on the first two occasions, his teacher arranged that he play the tenth juror in an adaptation of Twelve Angry Men. Although he took part in this play, he refused to attend a drama festival for which his teacher had also signed him up, as he saw himself as a football player and did not view acting as socially acceptable. His drama teacher persisted, and eventually persuaded him to join the National Youth Theatre in London.
After leaving school, Smith studied drama and creative writing at the University of East Anglia, graduating in 2005. His first theatre roles as part of the National Youth Theatre were Thomas Becket in Murder in the Cathedral and Bassoon in The Master and Margarita. His role in the latter earned him an agent and his first professional jobs, Fresh Kills and On the Shore of the Wide World. His new professional roles led him to seek an agreement with his university so that he could graduate without attending lectures in his final year.