Born in 1879. Johnstone began working at the Edinburgh Royal Maternity Hospital in 1920. In 1922 he became assistant gynaecologist at Edinburgh Royal Infirmary. He held the Chair of Midwifery at Edinburgh University from 1926-1946, and was President of the Royal College of Surgeons of Edinburgh from 1943-1945. Johnstone was author of a standard textbook on Midwifery. He was closely involved with the planning and building of the Simpson Memorial Maternity Hospital, and he subsequently became the first Chairman of the Board of Management of the Royal Infirmary of Edinburgh and Associated Hospitals. He died in 1969.