Medical and health pioneer. Born in Edinburgh, the son of a wealthy merchant, Littlejohn was educated at Perth Academy and the High School of Edinburgh. He was a graduate of the University of Edinburgh, later becoming Professor of Medical Jurisprudence (1897). As Edinburgh's first Medical Officer of Health (1862) he improved sanitation and instituted the legal requirement to notify occurrences of infectious diseases, allowing the authorities to act to prevent epidemics. This brought a dramatic drop in outbreaks of smallpox and typhus. He also served as President of the Royal College of Surgeons of Edinburgh (1875-6), President of the Medico-Chirurgical Society of Edinburgh (1883-5), and President of the Institute of Public Health (1893). He was awarded an honorary degree by the University of Edinburgh in 1893 and was knighted in 1895.
He retired from his chair in 1907 and was succeeded by his son, Professor Harvey Littlejohn (1862 - 1927), who was also a successful medical scientist. Littlejohn died at Arrochar (Argyll and Bute).