John Leech, the son of a Coffee House proprietor, was born in London on 29th August, 1817. He was educated at Charterhouse and at the age of sixteen he went to St. Bartholomew's to study medicine. Leech's teachers should became aware of Leech's superb anatomical drawings and began commissioning him to paint portraits.

Leech left medical school and tried to make a living from drawing and painting. His first known published work was a pamphlet called Etchings and Sketchings (1835) and included drawings of street characters such as cabmen, policemen, street musicians, etc. For the next few years he produced a series of humourous pamphlets including the Comic Latin Grammar, The Fiddle-Faddle Fashion Book and the Children of Mobility.

Although influenced by the work of James Gillray and George Cruikshank, Leech's humour was as one critic pointed out "less grotesque, less boisterous, less exaggerated, nearer to the truth and to ordinary experience." John Ruskin, the most important art critic of the time wrote: "John Leech's work contains the finest definition and natural history of the classes of our society; the kindest and the subtlest analysis of its foibles, the tenderest flattery of its pretty and well-bred ways, with which the modesty of subservient genius ever immortalised or amused careless masters."

1840 Leech was employed by the London Magazine to supply illustrations. The following year he was recruited by a new journal, Punch Magazine, founded by Mark Lemon and Henry Mayhew. Leech's humourous drawings were extremely popular and was one of the main reasons the magazine became a great success. Over the next twenty-three years the magazine published 3,000 of Leech's drawings and 600 cartoons.

A significant percentage of Leech's drawings dealt with political issues. Like the editors of the magazine, Lemon and Mayhew, Leech held fairly radical views. Between 1842 and 1845 Leech produced a series of cartoons such as Capital and Labour, Cheap Clothing and the Agricultural Question, which question the morality of the capitalist system. In the cartoon Substance and Shadow (1843), Leech criticised artists for ignoring social issues such as poverty.

John Leech, Capital and Labour, Punch Magazine, May, 1843)

Leech sympathized with those arguing for universal suffrage, however, like most liberals, he strongly opposed the arguments put forward by Feargus O'Conner and the Physical Force Chartists. Leech and Mark Lemon joined the 150,000 special constables recruited in April 1848, when the Chartists held their large Kennington Common demonstration. He wrote to a friend: "Mark Lemon and I were special constables on Monday last. You would have laughed to see us on duty, trying the area gates, etc. Mark continually finding excuses for taking a small glass of brandy and water. Policeman's duty is no joke. I had to patrol about from ten at night till one in the morning, and heartily sick of it I was. It was only my loyalty and extreme love of peace and order that made me stand it." The following week a section of the magazine was devoted to the Chartist rally. One drawing, showing a special constable who cannot remember if he supports or opposes the Chartists, probably reflects Leech's own views.

As well as providing drawings for Punch Magazine, Leech worked for several other publications including Bentley's Miscellany where he met Charles Dickens. As a result of this meeting Leech provided the drawings for Dickens' book The Christmas Carol.

In later life Leech suffered from angina and he had to give up strenuous exercise and also reduced his output of drawings. John Leech died of a heart attack at the age of 47 on 29 October, 1864. He is buried at Kensal Green, London.