In the year 1984, civilisation has been damaged by war, civil conflict, and revolution. Airstrip One (formerly known as Great Britain) is a province of Oceania, one of the three totalitarian super-states that rule the world. It is ruled by the "Party" under the ideology of "Ingsoc" (a newspeak shortening of "English Socialism") and the mysterious leader Big Brother, who has an intense cult of personality. The Party purges anyone who does not fully conform to their regime using the Thought Police and constant surveillance through devices such as Telescreens (two-way televisions).
Winston Smith is a member of the middle-class Outer Party, working at the Ministry of Truth, where he rewrites historical records to conform to the state's ever-changing version of history. Those who fall out of favour with the Party become "unpersons", disappearing with all evidence of their existence removed. Winston revises past editions of The Times, while the original documents are destroyed. He secretly opposes the Party's rule and dreams of rebellion, despite knowing that he is already a "thoughtcriminal" and likely to be caught one day.
While in a proletariat (prole) neighbourhood, he meets Mr. Charrington, the owner of an antiques shop, and buys a diary where he writes thoughts criticising the Party and Big Brother, and also writes that "if there is hope, it lies in the proles". To his dismay, when he visits a prole quarter he discovers they have no political consciousness. An old man he talks to there has no significant memory of life before the Revolution. As he works in the Ministry of Truth, he observes Julia, a young woman maintaining the novel-writing machines at the ministry, whom Winston suspects of being a spy against him, and develops an intense hatred of her. He vaguely suspects that his superior, an Inner Party official O'Brien, is part of an enigmatic underground resistance movement known as the Brotherhood, formed by Big Brother's reviled political rival Emmanuel Goldstein. Winston has a lunch conversation with a co-worker named Syme, who is writing a dictionary for a revised version of Newspeak, a controlled language of limited vocabulary. After Syme says freely that the true purpose of Newspeak is to reduce the capacity of human thought, Winston reflects that Syme will disappear as he is "too intelligent" and therefore dangerous to the Party.
One day, Julia secretly hands Winston a note confessing her love, and the two begin a torrid affair; an act of rebellion as the Party insists that sex is only for reproduction. Julia shares his loathing of the Party, but later realizes that she is disinterested in politics or in overthrowing the regime, thinking it impossible. They at first rendezvous in the country, and later meet in a rented room above Mr. Charrington's shop. During his affair with Julia, Winston remembers the disappearance of his family during the civil war of the 1950s and his terse relationship with his wife Katharine, from whom he is separated (divorce is not permitted by the Party). He also notices the disappearance of Syme during one of his working days. Weeks later, Winston is approached by O'Brien, who invites Winston over to his flat, which is noted as being of far higher quality than Winston's. O'Brien introduces himself as a member of the Brotherhood and sends Winston a copy of The Theory and Practice of Oligarchical Collectivism by Goldstein. Meanwhile, during the nation's Hate Week, Oceania's enemy suddenly changes from Eurasia to Eastasia, with no-one seemingly noticing the shift. Winston and Julia read parts of the book, which explains more about how the Party maintains power, the true meanings of its slogans and the concept of perpetual war. It argues that the Party can be overthrown if proles rise up against it. However, to Winston, it does not answer 'why' the Party maintains power.
Winston and Julia are captured and imprisoned. Mr. Charrington is revealed to be an agent of the Thought Police. At the Ministry of Love, Winston briefly interacts with colleagues who have been arrested for other offences. O'Brien arrives, revealing himself to be a Thought Police agent part of a special sting operation to catch "thoughtcriminals". Over several months, Winston is starved and tortured and forced to "cure" himself of his "insanity" by changing his own perception to fit in line with the Party. O'Brien reveals to Winston that the Party "seeks power for its own sake." When he taunts Winston by asking him if there is any humiliation which he has not yet been made to suffer, Winston points out that the Party has not managed to make him betray Julia, even after he accepted that the party is invincible and ‘objective truth’ has no meaning. He fantasizes that moments before his execution his heretic side will emerge, which, as long as he is killed while unrepentant, will be his great victory over the party. O'Brien says that once Winston is fully loyal, he will be released back into society for an unspecified period of time, and then he will be executed.
O'Brien takes Winston to Room 101 for the final stage of re-education, which contains each prisoner's worst fear. Confronted with a wire cage holding frenzied rats in his face (Winston's fear is rats), Winston willingly betrays Julia. Winston is released, takes up a sinecure and frequents the Chestnut Café. One day, Winston encounters Julia, who has also been tortured and both reveal betraying the other and having no feelings with each other. Back in the café, a news alert sounds and celebrates Oceania's supposed massive victory over Eurasian armies in Africa. Winston looks at the portrait of Big Brother, realising his full conversion, and reflects that "He loved Big Brother".