The novel begins with the affable, intrusive narrator outlining the nature of our hero. Joseph Andrews is the brother of Richardson's Pamela and is of the same rustic parentage and patchy ancestry. At the age of ten years he found himself tending to animals as an apprentice to Sir Thomas Booby. It was in proving his worth as a horseman that he first caught the eye of Sir Thomas's wife, Lady Booby, who employed him (now seventeen) as her footman.
After the death of Sir Thomas, Joseph finds that his Lady's affections have redoubled as she offers herself to him in her chamber while on a trip to London. In a scene analogous to many of Pamela's refusals of Mr B in Richardson's novel, however, Lady Booby finds that Joseph's Christian commitment to chastity before marriage is unwavering. After suffering the Lady's fury, Joseph dispatches a letter to his sister very much typical of Pamela's anguished missives in her own novel. The Lady calls him once again to her chamber and makes one last withering attempt at seduction before dismissing him from both his job and his lodgings.
With Joseph setting out from London by moonlight, the narrator introduces the reader to the heroine of the novel, Fanny Goodwill. A poor illiterate girl of 'extraordinary beauty' (I, xi) now living with a farmer close to Lady Booby's parish, she and Joseph had grown ever closer since their childhood, before their local parson and mentor, Abraham Adams, recommended that they postpone marriage until they have the means to live comfortably.
On his way to see Fanny, Joseph is mugged and laid up in a nearby inn where, by dint of circumstance, he is reconciled with Adams, who is on his way to London to sell three volumes of his sermons. The thief, too, is found and brought to the inn (only to escape later that night), and Joseph is reunited with his possessions. Adams and Joseph catch up with each other, and the parson, in spite of his own poverty, offers his last 9s 3½d to Joseph's disposal.
Joseph and Adams’ stay in the inn is capped by one of the many burlesque, slapstick digressions in the novel. Betty, the inn's 21-year-old chambermaid, had taken a liking to Joseph since he arrived; a liking doomed to inevitable disappointment by Joseph's constancy to Fanny. The landlord, Mr Tow-wouse, had always admired Betty and saw this disappointment as an opportunity to take advantage. Locked in an embrace, they are discovered by the choleric Mrs Tow-wouse, who chases the maid through the house before Adams is forced to restrain her. With the landlord promising not to transgress again, his lady allows him to make his peace at the cost of ‘quietly and contentedly bearing to be reminded of his transgressions, as a kind of penance, once or twice a day, during the residue of his life’ (I, xviii).
During his stay in the inn, Adams’ hopes for his sermons are mocked in a discussion with a traveling bookseller and another parson. Nevertheless, Adams remains resolved to continue his journey to London until it is revealed that his wife, deciding that he would be more in need of shirts than sermons on his journey, has neglected to pack them. The pair thus decide to return to the parson's parish: Joseph in search of Fanny, and Adams in search of his sermons.
With Joseph following on horseback, Adams finds himself sharing a stagecoach with an anonymous lady and Madam Slipslop, an admirer of Joseph's and a servant of Lady Booby. When they pass the house of a teenage girl named Leonora, the anonymous lady is reminded of a story and begins one of the novel's three interpolated tales, ‘The History of Leonora, or the Unfortunate Jilt’. The story of Leonora continues for a number of chapters, punctuated by the questions and interruptions of the other passengers.
After stopping at an inn, Adams relinquishes his seat to Joseph and, forgetting his horse, embarks ahead on foot. Finding himself some time ahead of his friend, Adams rests by the side of the road where he becomes so engaged in conversation with a fellow traveller that he misses the stagecoach as it passes. As the night falls and Adams and the stranger discourse on courage and duty, a shriek is heard. The stranger, having seconds earlier lauded the virtues of bravery and chivalry, makes his excuses and flees the scene without turning back. Adams, however, rushes to the girl's aid and after a mock-epic struggle knocks her attacker unconscious. In spite of Adams’ good intentions, he and the girl, who reveals herself to be none other than Fanny Goodwill (in search of Joseph after hearing of his mugging), find themselves accused of assault and robbery.
After some comic litigious wrangling before the local magistrate, the pair are eventually released and depart shortly after midnight in search of Joseph. They do not have to walk far before a storm forces them into the same inn that Joseph and Slipslop have chosen for the night. Slipslop, her jealousy ignited by seeing the two lovers reunited, departs angrily. When Adams, Joseph and Fanny come to leave the following morning, they find their departure delayed by an inability to settle the bill, and, with Adams’ solicitations of a loan from the local parson and his wealthy parishioners failing, it falls on a local pedlar to rescue the trio by loaning them his last 6s 6d.
The solicitations of charity that Adams is forced to make, and the complications which surround their stay in the parish, bring him into contact with many local squires, gentlemen and parsons, and much of the latter portion of Book II is occupied with the discussions of literature, religion, philosophy and trade which result.
The three depart the inn by night, and it is not long before Fanny needs to rest. With the party silent, they overhear approaching voices agree on 'the murder of any one they meet' (III, ii) and flee to a local house. Inviting them in, the owner, Mr Wilson, informs them that the gang of supposed murderers were in fact sheep-stealers, intent more on the killing of livestock than of Adams and his friends. The party being settled, Wilson begins the novel's most lengthy interpolated tale by recounting his life story; a story which bears a notable resemblance to Fielding's own young adulthood.
At the age of 16, Wilson's father died and left him a modest fortune. Finding himself the master of his own destiny, he left school and travelled to London where he soon acquainted himself with the dress, manners and reputation for womanising necessary to consider himself a ‘beau’. Wilson's life in the town is a façade: he writes love-letters to himself, obtains his fine clothes on credit and is concerned more with being seen at the theatre than with watching the play. After two bad experiences with women, he is financially crippled and, much like Fielding himself, falls into the company of a group of Deists, freethinkers and gamblers. Finding himself in debt, he turns to the writing of plays and hack journalism to alleviate his financial burden (again, much like the author himself). He spends his last few pence on a lottery ticket but, with no reliable income, is soon forced to exchange it for food. While in jail for his debts, news reaches him that the ticket he gave away has won a £3,000 prize. His disappointment is short-lived, however, as the daughter of the winner hears of his plight, pays off his debts, and, after a brief courtship, agrees to become his wife.
Wilson had found himself at the mercy of many of the social ills that Fielding had written about in his journalism: the over-saturated and abused literary market, the exploitative state lottery, and regressive laws which sanctioned imprisonment for small debts. Having seen the corrupting influence of wealth and the town, he retires with his new wife to the rural solitude in which Adams, Fanny and Joseph now find them. The only break in his contentment, and one which will turn out to be significant to the plot, was the kidnapping of his eldest son, whom he has not seen since.
Wilson promises to visit Adams when he passes through his parish, and after another mock-epic battle on the road, this time with a party of hunting dogs, the trio proceed to the house of a local squire, where Fielding illustrates another contemporary social ill by having Adams subjected to a humiliating roasting. Enraged, the three depart to the nearest inn to find that, while at the squire's house, they had been robbed of their last half-guinea. To compound their misery, the squire has Adams and Joseph accused of kidnapping Fanny, to have them detained while he orders the abduction of the girl himself. She is rescued in transit, however, by Lady Booby's steward, Peter Pounce, and all four of them complete the remainder of the journey to Booby Hall together.
On seeing Joseph arrive back in the parish, a jealous Lady Booby meanders through emotions as diverse as rage, pity, hatred, pride and love. The next morning Joseph and Fanny's banns are published and the Lady turns her anger onto Parson Adams, who is accommodating Fanny at his house. Finding herself powerless either to stop the marriage or to expel them from the parish, she enlists the help of Lawyer Scout, who brings a spurious charge of larceny against Joseph and Fanny to prevent, or at least postpone, the wedding.
Three days later, the Lady's plans are foiled by the visit of her nephew, Mr Booby, and a surprise guest: Booby has married Pamela, granting Joseph a powerful new ally and brother-in-law. What is more, Booby is an acquaintance of the justice presiding over Joseph and Fanny's trial, and instead of Bridewell, has them committed to his own custody. Knowing of his sister's antipathy to the two lovers, Booby offers to reunite Joseph with his sister and take him and Fanny into his own parish and his own family.
In a discourse with Joseph on stoicism and fatalism, Adams instructs his friend to submit to the will of God and control his passions, even in the face of overwhelming tragedy. In the kind of cruel juxtaposition usually reserved for Fielding's less savoury characters, Adams is informed that his youngest son, Jacky, has drowned. After indulging his grief in a manner contrary to his lecture a few minutes previously, Adams is informed that the report was premature, and that his son had in fact been rescued by the same pedlar that loaned him his last few shillings in Book II.
Lady Booby, in a last-ditch attempt to sabotage the marriage, brings a young beau named Didapper to Adams’ house to seduce Fanny. Fanny is unattracted to his bold attempts of courtship. Didapper is a little too bold in his approach and provokes Joseph into a fight. The Lady and the beau depart in disgust, but the pedlar, having seen the Lady, is compelled to relate a tale. The pedlar had met his wife while in the army, and she died young. While on her death bed, she confessed that she once stole an exquisitely beautiful baby girl from a family named Andrews, and sold her on to Sir Thomas Booby, thus raising the possibility that Fanny may in fact be Joseph's sister. The company is shocked, but there is general relief that the crime of incest may have been narrowly averted.
The following morning, Joseph and Pamela's parents arrive, and, together with the pedlar and Adams, they piece together the question of Fanny's parentage. The Andrews identify her as their lost daughter, but have a twist to add to the tale: when Fanny was an infant, she was indeed stolen from her parents, but the thieves left behind a sickly infant Joseph in return, who was raised as their own. It is immediately apparent that Joseph is the above-mentioned kidnapped son of Wilson, and when Wilson arrives on his promised visit, he identifies Joseph by a birthmark on his chest. Joseph is now the son of a respected gentleman, Fanny an in-law of the Booby family, and the couple no longer suspected of being siblings. Two days later they are married by Adams in a humble ceremony, and the narrator, after bringing the story to a close, and in a disparaging allusion to Richardson, assures the reader that there will be no sequel.