Born on 4 July 1890 at West Hartlepool, Durham, where his father Thomas George Ainsley (MRCS 1877, MD Durham) was in practice. His mother's maiden name was Hill. He was educated at Malvern College, at Caius College, Cambridge, where he took second-class honours in the Natural Sciences Tripos, part 1, 1912, and at the London Hospital, where he was a house surgeon. He qualified in 1915, was immediately commissioned in the RAMC, and went on active service in the Near East. He was promoted Captain, and won the Military Cross in 1918. After taking the Fellowship in 1922 he joined his father and his uncle Henry Moncrieff Macgill (MD Edinburgh) in general practice at West Hartlepool. Later, his brother-in-law James Elmsly Mitchell (MD Aberdeen) joined the partnership. Ainsley was surgeon to the Cameron Hospital and at one time medical superintendent of the General Hospital. He was for a short time orthopaedic surgeon to the Hartlepool hospitals and, on the formation of the National Health Service, he became surgical consultant to the West Hartlepool group of hospitals in 1948. He retired in 1957, after long filling a prominent place in the professional life of his native town. He had been chairman of the Hartlepools division of the British Medical Association in 1933-34 and president of the Tees-side branch in 1954. He died on 16 February 1960 aged 69, at 60 Clifton Avenue, West Hartlepool. Ainsley married Dr Roberta Frances Dunbar Hutchison, MB BCh Edinburgh, who survived him, but without children. His recreations were golf and loch-fishing in Scotland, though he was strongly opposed to the killing of animals in sport and even to the use of animals in the laboratory.