 Wynn-Williams was born at 'Glasfryn' in Swansea, Glamorganshire, Wales, on 5 March 1903.He was the eldest child of William Williams (1863–1945), a physics teacher and later divisional inspector of schools for north and mid-Wales, and Mary Ellen Wynn (1907–1935), known as Nell, daughter of Robert Wynn, a shopkeeper in Llanrwst.His education was at Grove Park School in Wrexham, and, from 1920, at Bangor University, where he graduated in 1923.