Allworthy apologizes to Tom for his past behavior. Tom says that there is no need for retribution; the joy he is experiencing now atones for his suffering. Tom laments his follies and vices, but Allworthy brushes them away, praising Tom for not being a hypocrite. Allworthy tells Tom that he has visited Sophia, and urges Tom to submit to Sophia's will. Mrs. Miller meets with Tom and tells him that she has explained to Sophia that Tom's proposal letter to Lady Bellaston was not meant seriously. Sophia still complained that Tom was a "Libertine," but Mrs. Miller told her that Tom turned down Mrs. Hunt. Mr. Western arrives, extremely impatient for the afternoon courtship festivities.
Jones tells Allworthy and Mrs. Miller how he gained his liberty from the prison. Mrs. Waters assured Fitzpatrick that Tom did not have an affair with his wife and, consequently, Fitzpatrick admitted that he initiated the duel. Moreover, Fitzpatrick is so delighted with what Mrs. Waters has told him that he praises Tom to Lord Fellamar, who decides that he should assist this man whom he affronted by his advances to Sophia.
Allworthy wishes to punish Blifil, but Tom argues for forgiveness. Mrs. Miller and Allworthy want Blifil to leave the house as soon as possible. Tom asks that he may be the messenger of the news. He finds Blifil bawling on his bed, although Blifil is frightened rather than contrite. Tom tells Blifil the news—he comforts Blifil and offers to provide for him. Blifil thanks Tom profusely, then departs. Allworthy reveals Black George's corruption to Tom. Tom tells Allworthy of Black George's generosity to him while he was in prison, but Allworthy is determined to punish Black George for his dishonesty. Partridge and Tom are reunited.
Tom meets Sophia at Western's house. They are both finely dressed and look breathtaking. At first they remain silent. Sophia suggests that Tom judge his own behavior—she tells him that only time will prove whether he can cast aside his wild desires. She does not understand how he could have been unchaste in Upton. Tom argues that the delicacy of women prevents them from imagining how sordid men can be. He argues that amours of the body do not affect the amour of the heart. Sophia accepts his reply, but says that she will only marry him after twelve months. They kiss. Mr. Western bursts in and, after teasing the lovers with bawdy jokes, orders Sophia to marry Tom immediately. Sophia says that she cannot disobey her father. Western looks forward to having a grandson in nine months.
The wedding is filled with mirth, and those who were unhappy before are happy now. The narrator summarizes the future. Tom makes Allworthy agree to give Blifil an annuity of 200 pounds, even though Allworthy refuses to speak to Blifil. Blifil converts to Methodism in the hopes of marrying a rich Methodist widow who lives near to him. Mrs. Fitzpatrick separates from Fitzpatrick. Mrs. Waters marries Parson Supple, and Allworthy grants her an annuity of sixty pounds. Partridge sets up a school with the help of Tom. He is engaged to Molly Seagrim. Sophia and Tom now live on Western's estate and have two children, a boy and a girl. Western has retired to a smaller estate, but visits the couple frequently. Tom has conquered his cheeky streak. He and Sophia are still very much in love, and hold each other in the highest esteem. They show kindness and respect to all around them.
Book XVIII follows the archetypal comic finale in that it consists of the resolution of a series of misunderstandings: Square's letter dispels Blifil's false accusations, and Mrs. Waters's testimony reveals Tom's true parentage.
The summary of future events that concludes the novel is typical of Romantic comedy, and it serves to show which characters have experienced a "Revolution," and which ones have not. Blifil, for example, shows no contrition about his wicked acts and instead begins plotting afresh. It is appropriate that Tom, the protagonist, has undergone the greatest transformation—he now lives in perfect chastity with Sophia as his wife. Tom's forgiveness of Blifil makes Tom a better man even than Allworthy, who wishes to punish Blifil. In such a way, rather than simply being born good, Tom achieves the status of "hero" by the novel's end. The vast arc that Tom makes from beggarly bastard to wealthy, dignified gentleman makes the novel a kind of Bildungsroman"—that is, a novel that charters the growth of a single character from infancy to maturity.