He was born in Newington, Edinburgh in 1879, the son of Rev William Johnstone DD and his wife Janet (née Brocon).

After schooling at George Watson's College, Edinburgh he entered Faculty of Arts at the University of Edinburgh, qualifying MA in 1900 and, having entered the faculty of Medicine, qualified MBChB with honours three years later.

[2] After resident posts in Edinburgh he had decided on a career in obstetrics, working initially at the Vienna clinic of Ernst Wertheim, the pioneer of radical hysterectomy.

[2] During World War I he served as medical officer in the Royal Victoria (Red Cross) Hospital in Edinburgh.

[4] From 1926 to 1946 he was Professor of Midwifery and Gynaecology at Edinburgh University[5] succeeding Benjamin Philip Watson.

[6] His main contributions to the literature were his Textbook of Midwifery for Students and Practitioners, first published in 1913 and which, by the time of his death had run to a remarkable 21 editions.