In May 1827, the Pickwick Club of London, headed by Samuel Pickwick, decides to establish a traveling society in which four members journey about England and make reports on their travels. The four members are Mr. Pickwick, a kindly retired businessman and philosopher whose thoughts never rise above the commonplace; Tracy Tupman, a ladies' man who never makes a conquest; Augustus Snodgrass, a poet who never writes a poem; and Nathaniel Winkle, a sportsman of tremendous ineptitude.
The Pickwickians meet to begin their first journey and get knocked about by an angry cabman, who thinks they are informers, while an angry crowd gathers. They are rescued by Alfred Jingle, who travels with them to Rochester. Jingle is an adventurer interested in wealthy women, and on this first trip he involves the innocent Winkle in a duel with Dr. Slammer, a hot-tempered army man.
At Chatham, the Pickwickians watch army maneuvers, get buffeted about, and meet Mr. Wardle, a country squire who invites them to his estate at Dingley Dell. After some mishaps with horses, Mr. Pickwick and his friends arrive at Mr. Wardle's Manor Farm, where they enjoy card games, flirting, storytelling, hunting, and a cricket match. Mr. Tupman falls in love with Mr. Wardle's spinster sister, Rachael; and Mr. Snodgrass falls in love with his daughter, Emily. However, Tupman is outsmarted by the vivacious, unscrupulous Jingle, who elopes with Rachael. Mr. Pickwick and Mr. Wardle pursue Jingle and Rachael to London, where, with the help of a lawyer, Mr. Perker, they buy off Jingle and save Rachael Wardle from an unhappy marriage.
In London Mr. Pickwick comes across Sam Weller, a boot cleaner and general handyman whom he takes on as a valet. Sam is a cockney man of the world: witty, intelligent, handy with his fists. When Mr. Pickwick tells his widowed landlady, Mrs. Bardell, that he has taken on a servant, she assumes from the ambiguous way he puts it that he intends to marry her. Mrs. Bardell faints in his arms just as Tupman, Snodgrass, and Winkle enter — a compromising circumstance.
Sam Weller's father, Tony, a coachman who had the misfortune to marry a widow, provides a running commentary through the novel on the dangers of matrimony. Tony's wife has taken up with a hypocritical, alcoholic evangelist and makes life miserable for her husband until her death. Both Tony Weller and Mr. Pickwick are prey for widows, because Mrs. Bardell soon starts a breach-of-promise suit against Mr. Pickwick.
Meanwhile, Mr. Pickwick and his friends go to Eatanswill to witness an election, which is both violent and nonsensical. Mr. Pickwick and Winkle stay with Mr. Pott, the editor of a partisan newspaper, and Winkle unwittingly becomes involved in Pott's domestic fights. During their visit to Eatanswill the Pickwickians are invited to a costume party given by the local literary lioness, Mrs. Leo Hunter, where several varieties of silliness are exhibited. At this party Mr. Pickwick sees Alfred Jingle, whom he pursues to a neighboring town. Jingle's servant tells Mr. Pickwick that Jingle has designs on a young lady at a boarding school, and Mr. Pickwick decides to prevent the elopement. However, this information is a ruse that leads to Mr. Pickwick's embarrassment and an attack of rheumatism. The Pickwickians assemble at Bury St. Edmunds, where Mr. Wardle is on a hunting trip, and Mr. Pickwick recovers enough to go along. There he learns that Mrs. Bardell has filed suit against him through Dodson and Fogg, a pair of rascally lawyers. So Mr. Pickwick returns to London to see about getting legal help.
In London, Mr. Pickwick learns that Jingle is in Ipswich and goes there to expose him. Because of a mix-up in bedrooms at an Ipswich Inn Mr. Pickwick is hauled before the justice, a local henpecked tyrant called Mr. Nupkins. Nupkins is visited frequently by Jingle, who is interested in the daughter. Mr. Pickwick extricates himself by proving that Jingle is an adventurer.
Eventually the Pickwickians return to the Wardle farm to celebrate Christmas and the wedding of Mr. Wardle's daughter, Isabella. Amid festivities Snodgrass continues his romance with Emily, and Winkle falls in love with Arabella Allen, a friend of Mr. Wardle's daughters.
On Valentine's Day, 1831, Mr. Pickwick is tried for breach of promise. Due to the rhetorical allegations of Serjeant Buzfuz and to the circumstantial evidence, Mr. Pickwick is found guilty and ordered to pay damages, which he refuses to do.
Since it is two months before Dodson and Fogg can have him jailed, the Pickwickians make a trip to Bath. There Winkle gets into more difficulties over a middle-aged woman and flees to Bristol, where he learns that his sweetheart, Arabella Allen, has been hidden by her brother. Sam Weller and Mr. Pickwick arrive in Bristol, where they help Winkle find Arabella in order to declare his intentions.
On returning to London, Mr. Pickwick is taken to the Fleet Prison for debtors because he will not pay damages. In prison he witnesses much misery, filth, and squalor and for a brief time he is victimized by two predatory inmates. There he finds Alfred Jingle and his servant in utter destitution and gives them some assistance. Mr. Pickwick tells Sam Weller to leave him, but Sam has himself jailed for debt to be with his kindly master. Dismayed by the misery of prison, Mr. Pickwick rents a cell by himself and comes out only in the evenings. When Mrs. Bardell is arrested and jailed because she cannot pay her lawyers, Mr. Pickwick begins to soften. Further, Winkle has married Arabella and needs Mr. Pickwick to intercede for them with her brother and his own father. Finally Mr. Pickwick decides to pay costs, which releases himself and Mrs. Bardell, and he also pays Jingle's debts.
Mr. Pickwick goes to Bristol to tell Ben Allen about Arabella's marriage, and Ben adjusts to the fact with the help of much liquor. Mr. Pickwick then goes to Birmingham to tell Winkle's father, who appears angry and disgusted by the news.
Back in London Mr. Pickwick pays Dodson and Fogg, sends Jingle and his servant to the West Indies to begin afresh, and learns that Emily Wardle is planning to elope with Snodgrass. Mr. Pickwick convinces Mr. Wardle that Snodgrass is a worthy gentleman, and the couple are married in Mr. Pickwick's newly purchased home. In the meantime Sam Weller has been courting a pretty housemaid named Mary, and under Mr. Pickwick's auspices they are married. And, though the London Pickwick Club has been dissolved, Samuel Pickwick lives to be godfather to many children.