Snow was a British physician who is considered one of the founders of epidemiology for his work identifying the source of a cholera outbreak in 1854.

John Snow was born into a labourer's family on 15 March 1813 in York and at 14 was apprenticed to a surgeon. In 1836, he moved to London to start his formal medical education. He became a member of the Royal College of Surgeons in 1838, graduated from the University of London in 1844 and was admitted to the Royal College of Physicians in 1850.

At the time, it was assumed that cholera was airborne. However, Snow did not accept this 'miasma' (bad air) theory, arguing that in fact entered the body through the mouth. He published his ideas in an essay 'On the Mode of Communication of Cholera' in 1849. A few years later, Snow was able to prove his theory in dramatic circumstances. In August 1854, a cholera outbreak occurred in Soho. After careful investigation, including plotting cases of cholera on a map of the area, Snow was able to identify a water pump in Broad (now Broadwick) Street as the source of the disease. He had the handle of the pump removed, and cases of cholera immediately began to diminish. However, Snow's 'germ' theory of disease was not widely accepted until the 1860s.

Snow was also a pioneer in the field of anaesthetics. By testing the effects of controlled doses of ether and chloroform on animals and on humans, he made those drugs safer and more effective. In April 1853, he was responsible for giving chloroform to Queen Victoria at the birth of her son Leopold, and performed the same task in April 1857 when her daughter Beatrice was born.

Snow died of a stroke on 16 June 1858.