Butt who was a physician to Henry VIII,[2] his older brother was the poet, historian and senior Civil Servant Sir Stanley Mordaunt Leathes.

Rejecting his father's wishes to become ordained in the Church of England, Leathes instead studied Medicine at Guy's Hospital, walking 12 miles there and back each day from his aunt's home in Highgate.

[2] In 1909 he became Honorary Secretary of The Physiological Society, but had to resign the post when he moved to Canada later in the year when he was appointed to the newly created Chair in Pathological Chemistry at the University of Toronto.

He remained in Toronto until 1914 when he returned to the UK to take up the post of Professor of Physiology at the University of Sheffield, where he also served two terms as Dean of the Faculty of Medicine.

[2] After leaving Sheffield Leathes moved firstly to Wantage and then to the University of Oxford where he worked for a short period with Professor John Mellanby, FRS in the laboratory of physiology; however, this activity was curtailed with the outbreak of World War II in 1939, when Leathes retired successively to Lyme Regis, London and Southbourne, finally settling after the war in Montreux in Switzerland where he died in September 1956 aged 92.