During March 1737, Johnson lived in London with his former pupil the actor David Garrick. Garrick had connections in London, and the two stayed with his distant relative, Richard Norris, who lived in Exeter Street. Johnson did not stay there long, and set out to Greenwich near the Golden Hart Tavern to finish his play, Irene. Later, in October 1737, Johnson brought his wife to London; they first lived at Woodstock Street and then moved to 6 Castle Street. Soon, Johnson found employment with Edward Cave, and wrote for his The Gentleman's Magazine.

According to Walter Jackson Bate, his work for the magazine and other publishers "is almost unparalleled in range and variety", and "so numerous, so varied and scattered" that "Johnson himself could not make a complete list". During this time, Johnson was exposed to the "imitations" of Horace composed by Pope and saw how they were used to attack contemporary political corruption. Both the form and subject were popular, and Johnson decided to follow Pope's lead by creating his own imitation.

In May 1738, London was published anonymously, and it went into a second edition that year. This was his first major work to be published to a wide audience and one of his longest "non-dramatic public poems". It was not written to be a general satire; instead, it was written to demonstrate Johnson's skill as a writer and to become popular in order to further his literary career.

London is part of the eighteenth-century genre of imitation. The work was based on Juvenal's Third Satire which describes Umbricius leaving Rome to live in Cumae in order to escape from the vices and dangers of the capital city. In Johnson's version, it is Thales who travels to Cambria (Wales) in order to escape from the problems of London. Johnson chose Juvenal as a model based on his own appreciation for Juvenal's works.

The poem describes the various problems of London, including an emphasis on crime, corruption, and the squalor of the poor. In order to emphasize his message, these various abstract problems are personified as beings that seek to destroy London. Thus, the characters of Malice, Rapine, and Accident "conspire" (line 13) to attack those who live in London.

The poem begins:

Though grief and fondness in my breast rebel,

When injured Thales bids the town farewell,

Yet still my calmer thoughts his choice commend,

I praise the hermit, but regret the friend,

Resolved at length, from vice and London far,

To breathe in distant fields a purer air,

And, fixed on Cambria's solitary shore,

Give to St David one true Briton more.

:(lines 1–8)

Who Thales represents is unknown, but it is possible that he represents Richard Savage, Johnson's friend who left London to travel to Wales.

The main emphasis of the poem comes to light on line 177: "Slow rises worth, by poverty depressed".

The poem is forced to cut short, and the narrator concludes:

Much could I add, — but see the boat at hand,

The tide retiring, calls me from the land:

Farewell! — When youth, and health, and fortune spent,

Thou fly'st for refuge to the wilds of Kent;

And tired like me with follies and with crimes,

In angry numbers warn'st succeeding times;

Then shall thy friend, nor thou refuse his aid,

Still foe to vice, forsake his Cambrian shade;

In virtue's cause once more exert his rage,

Thy satire point, and animate thy page.

:(lines 254–263)

Politics

The content of London was opposed to the government of England under the Whig Sir Robert Walpole during the time that Johnson lived in London. The poem does not hide that it has a political agenda, and the lines directed against George II follow a Jacobite political sentiment. Although he does not mention George in line 50 ("Let ____ live here, for ____ has learned to live"), he is referring to the king. Not until the end of the poem does the narrator directly address the government when he says:

Propose your schemes, ye Senatorian band,

Whose Ways and Means support the sinking land;

Lest ropes be wanting in the tempting spring,

To rig another convoy for the K__g.

:(lines 244–247)

It is through the "Ways and Means", or the Committee of Ways and Means of the House of Commons, that the king is able to tax the people, and this function is part of many that Johnson satirises.

The city of London was seen as a means to attack the Whig political party which was run by Robert Walpole. In particular, Johnson compares the actions of George II and Walpole to those of the Roman emperors during the decline of the Roman Empire. Part of the attack included, as Brean Hammond puts it, "a nostalgic glorification of English history that went hand-in-hand with the representation of the present as in the grip of forms of corruption never previously encountered". This "nostalgic glorification" includes multiple references to Queen Elizabeth and her defeat of the Spanish invaders while simultaneously claiming that Walpole is seeking to allow Spain to conquer England's trade investments.

Johnson judged his own poem harshly; he revised it in 1748 and came to depreciate the genre of poetic imitations of which London was a member. Another aspect of the poem that Johnson disliked in his later years was the pastoral bias of the poem, to prefer the countryside to the city. However, his contemporaries did not agree with his later assessment, and Alexander Pope from the first claimed that the author "will soon be déterré", although it did not immediately happen. This would be the second time that Pope directly praised a work of Johnson. Not everyone praised the work, as its political themes did cause controversy within the Hanoverian government and with the supporters of Walpole's administration. Johnson was not to receive recognition as a major literary figure until a few years later when he began to work on his A Dictionary of the English Language.

The printer and bookseller Robert Dodsley bought the copyright from Johnson for £10. Later, London would be rated as his second greatest poem, as The Vanity of Human Wishes would replace it in the eyes of Walter Scott and T. S. Eliot. The later critic, Howard Weinbrot, agreed with Scott's and Eliot's assessment and says "London is well worth reading, but The Vanity of Human Wishes is one of the great poems in the English language." Likewise, Robert Folkeflik says, "It is not Johnson's greatest poem, only because The Vanity of Human Wishes is better". Some critics, like Brean Hammond, only see the poem as "no better than a somewhat mechanical updating of Juvenal's third Satire." Others, like Walter Jackson Bate consider the poem as "masterly in its versification".