James (Jim) Walsh was born on 25 August 1932 at Belleek on the Fermanagh–Donegal border. He showed early academic promise by winning a scholarship at St Columb's College, Derry, where he had commenced studies in 1945. By 1950 he had begun to study medicine at the Queen's University of Belfast, graduating in 1956, and completing his intern year at the Mater Infirmorum Hospital in Belfast.

John Gwilym was born in 1918 and was brought up in Holyhead, Anglesey, within the characteristic culture of North Wales, which in his boyhood was still relatively unaffected by modernisation. His father introduced him to country sports, but his mother diverted him towards more intellectual interests; however, she died when Gwilym was 15, which affected him deeply. At his grammar school, where he was captain of cricket, he received a good grounding in science subjects but was uncertain about his future direction.