BSc (anatomy and physiology) Manch 1938, MB ChB 1942; DMRD 1950.
McMyn was born in Accrington on 31 October 1916. He was educated at Manchester Grammar School and at the University of Manchester. McMyn held junior appointments at Clatterbridge General Hospital, Cheshire, and Smithdown Road Hospital, Liverpool. From 1943 to 1947 McMyn served as a medical officer in the Emergency Medical Service, at Winwick and Baguley Hospitals. He then served in the RAMC before undertaking the DMRD course at Manchester. McMyn was registrar at Oldham Royal Infirmary x-ray department, before emigrating to Australia as a radiologist.