James Jemson was born in Nateby, Lancashire, on 12 December 1900, the third child of John Jemson, a farmer, and Margaret, née Gorst. He was educated at Nateby School, Garstang, and at Kirkham Grammar School before entering Guy's Hospital Medical School. After qualifying in 1923 he was clinical assistant to Sir Heneage Ogilvie before being appointed house surgeon and casualty officer at the Royal Berkshire Hospital, Reading. He was then employed by the Greenwich and Deptford Institution (later St Alfege's Hospital) and while there contracted diphtheria, complicated by myocarditis and peripheral neuritis. He passed the FRCS in 1933. Shortly before the war he was appointed deputy superintendent of St Alfege's and after the outbreak of war was superintendent of St Peter's Hospital, London, which was destroyed in the air raids. He was then superintendent of St Charles' Hospital, Ladbroke Grove, until 1944 when he was appointed surgical specialist at Lewisham Hospital. In 1948 with the advent of the National Health Service he became consultant surgeon until his retirement in 1964. He then moved to Bishop's Cannings, near Devizes. In 1928 he married Janet Mildred and they had two sons, the elder, John Armstrong Jemson, qualified at Guy's and is in general practice in British Columbia, and the younger is a veterinary surgeon. His wife predeceased him and he died in Calne, Wiltshire, on 15 December 1988, aged 88.