 Wyn-Harris was born in Acton, Middlesex on 24 August 1903 as Percy Wynne Harris (he formally changed his name to Percy Wyn-Harris in 1953).He was the son of a company director and was educated at Gresham's School, Holt, and Gonville and Caius College, Cambridge.As an undergraduate, he was a member of the University Mountaineering Club.