Benfield was born in Wanstead, Essex, the son of margarine sales representative Fred Turner and his wife Joan, née White.
He was educated at Loughton school, then the town's further education college; after four years as an ambulance driver in London, he studied history at the University of Nottingham, during which time he discovered a passion for acting with the drama society.
After training at the Webber Douglas Academy of Dramatic Art from 1976 to 1978, with there already an actor called "John Turner", he assumed the stage name "John Benfield", the surname coming from his mother's side.
[3] Benfield appeared in 75 television episodes or films starting in 1981 with small parts in BBC drama adaptations, such as The Winter's Tale and The Day of the Triffids.
Benfield lived in Oxfordshire with his wife, Lilian, née Lees.