Author. Born in Cardross (Argyll and Bute), Cronin was raised in humble circumstances following the death of his father. He was sent to Dumbarton Academy at the expense of his uncle. He trained in medicine although the First World War, during which he served as a surgeon in the Royal Navy, interrupted his studies. He completed his medical degree at the University of Glasgow in 1919 and moved to South Wales with his wife, who had been a fellow medical student. He practised for a time and, having been appointed Medical Inspector of Mines in 1924, began to investigate occupational diseases in the coal-mining industry. However, following illness he gave up his medical career to become an author. Cronin is best known for Adventures in Two Worlds (1952) which gave rise to the notable radio and TV series Dr Finlay's Casebook. Other notable works were Hatter's Castle (1931), The Stars Look Down (1935), The Citadel (1938) and The Keys of the Kingdom (1942), all of which were made into successful films.
In 1939, Cronin emigrated for the USA, but he returned to Europe some years later and died a tax exile in Montreux (Switzerland).