Stephens was born in Shirehampton, Bristol, in 1931. When aged 18, he won a scholarship to Esme Church's Bradford Civic Theatre School in Yorkshire, where he met his first wife Nora, a fellow student. His first professional engagement was with the Caryl Jenner Mobile Theatre, which he followed in 1951 by a year of more challenging parts in repertory at the Royalty Theatre, Morecambe, followed by seasons of touring and at the Hippodrome, Preston. The London Director Tony Richardson saw a performance at the Royalty and this led to an offer of a place in the "momentous" first season of English Stage Company at the Royal Court in 1956. His success was assured.