Educated at Bradford Grammar School, and King's College, Cambridge, he received his clinical training at the Westminster Hospital, where he was house physician and accoucheur from 1891 to 1893, and Bird Gold Medallist in 1893. Then followed a year at Great Ormond Street as house physician and house surgeon, and five years as house surgeon to Addenbrooke's Hospital, Cambridge. During this time he took the FRCS. Having joined the Fever Service of the Metropolitan Asylums Board in 1901 he was appointed medical superintendent to the Brook Hospital in 1909, and remained there until his retirement in 1933, except for a period in charge of the Western Hospital, Fulham, from 1923 to 1925, while the Brook Hospital was closed. The Brook Hospital became a military hospital during the first world war (1915-19), and John Byles was appointed officer in charge with the rank of Lieutenant-Colonel RAMC. During his service with the MAB he and Dr T F Ricketts published their book *The Diagnosis of Smallpox*, 1908. He was an expert photographer and gardener. He lived at 56 Southborough Road, Bickley, but died in the Brook Hospital, Shooter's Hill, Woolwich on 3 August 1964, aged 95, survived by his wife, son and daughter.