Balfour was a distinguished Scottish physician specializing in tropical medicine. He worked internationally, notably in Sudan where he was involved in public health and tropical disease research. Later in his career he became Director of the London School of Hygiene & Tropical Medicine and served on commissions related to colonial health and disease control. He was knighted in 1930.
In addition to his medical and public health work, Balfour wrote several adventure and historical novels influenced by H. Rider Haggard and Robert Louis Stevenson. The Golden Kingdom is among his better-known fiction works.