BSc Manch 1935, MB ChB 1941, MD 1948 (Gold Medal).
Slack was born in Redcar, Yorkshire, on 19 July 1913, and was educated at Manchester Grammar School and the University of Manchester, where he was editor of the Manchester University Medical Students Gazette. After qualifying, Slack held house appointments at MRI, he was supernumerary chief assistant to John F. Wilkinson in the Haematology Department, and later registrar. Slack was senior research assistant to the rheumatology research centre at the University of Manchester and MRI, before being appointed medical inspector for the Home Office. Slack was a fellow of Manchester Medical Society and a member of the Biochemical Society.