Snow was born on 15 March 1813 in York, England, the first of nine children born to William and Frances Snow in their North Street home, and was baptised at All Saints' Church, North Street, York. His father was a labourer who worked at a local coal yard, by the Ouse, constantly replenished from the Yorkshire coalfield by barges, but later was a farmer in a small village to the north of York.

The neighbourhood was one of the poorest in the city, and was frequently in danger of flooding because of its proximity to the River Ouse. Growing up, Snow experienced unsanitary conditions and contamination in his hometown. Most of the streets were unsanitary and the river was contaminated by runoff water from market squares, cemeteries and sewage.

From a young age, Snow demonstrated an aptitude for mathematics. In 1827, when he was 14, he obtained a medical apprenticeship with William Hardcastle in Newcastle-upon-Tyne. In 1832, during his time as a surgeon-apothecary apprentice, he encountered a cholera epidemic for the first time in Killingworth, a coal-mining village. Snow treated many victims of the disease and gained a lot of experience. Additionally, while he was an apprentice, Snow could not drink, gamble or marry. Eventually he adjusted to teetotalism and led a life characterized by abstinence, signing an abstinence pledge in 1835. Snow was also a vegetarian and tried to only drink distilled water that was “pure”. Between 1833 and 1836 Snow worked as an assistant to a colliery surgeon, first in Burnopfield, County Durham, and then in Pateley Bridge, West Riding of Yorkshire. In October 1836 he enrolled at the Hunterian school of medicine on Great Windmill Street, London.

In 1837, Snow began working at the Westminster Hospital. Admitted as a member of the Royal College of Surgeons of England on 2 May 1838, he graduated from the University of London in December 1844 and was admitted to the Royal College of Physicians in 1850. In 1850 he was also one of the founding members of the Epidemiological Society of London, formed in response to the cholera outbreak of 1849.

In 1857, Snow made an early and often overlooked contribution to epidemiology in a pamphlet, On the adulteration of bread as a cause of rickets.

John Snow was one of the first physicians to study and calculate dosages for the use of ether and chloroform as surgical anaesthetics, allowing patients to undergo surgical and obstetric procedures without the distress and pain they would otherwise experience. He designed the apparatus to safely administer ether to the patients and also designed a mask to administer chloroform. He personally administered chloroform to Queen Victoria when she gave birth to the last two of her nine children, Leopold in 1853 and Beatrice in 1857, leading to wider public acceptance of obstetric anaesthesia. Snow published an article on ether in 1847 entitled On the Inhalation of the Vapor of Ether. A longer version entitled On Chloroform and Other Anaesthetics and Their Action and Administration was published posthumously in 1858.

After finishing his medical studies in the University of London, he earned his MD in 1844. Snow set up his practice at 54 Frith Street in Soho as a surgeon and general practitioner. John Snow contributed to a wide range of medical concerns including anaesthesiology. He was a member of the Westminster Medical Society, an organisation dedicated to clinical and scientific demonstrations. Snow gained prestige and recognition all the while being able to experiment and pursue many of his scientific ideas. He was a speaker multiple times at the society’s meetings and he also wrote and published articles. He was especially interested on patients with respiratory diseases and tested his hypothesis through animal studies. In 1841, he wrote, On Asphyxiation, and on the Resuscitation of Still-Born Children, which is an article that discusses his discoveries on the physiology of neonatal respiration, oxygen consumption and the effects of body temperature change. Therefore, his interest in anaesthesia and breathing was evident since 1841 and beginning in 1843, Snow experimented with ether to see its effects on respiration. Only a year after ether was introduced to Britain, in 1847, he published a short work titled, On the Inhalation of the Vapor of Ether, which served as a guide for its use. At the same time, he worked on various papers that reported his clinical experience with anaesthesia, noting reactions, procedures and experiments.

Though he thoroughly worked with ether as an anaesthetic, he never attempted to patent it; instead he continued to work and publish written works on his observations and research. Within two years after ether was introduced, Snow was the most accomplished anaesthetist in Britain. London’s principal surgeons suddenly wanted his assistance.

John Snow also studied chloroform, as much as he studied ether, which was introduced in 1847 by James Young Simpson, a Scottish obstetrician.