In the year 1984, civilization has been damaged by world 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 brutally purges out anyone who does not fully conform to their regime using the Thought Police and constant surveillance through telescreens (two-way televisions), cameras, and hidden microphones. Those who fall out of favour with the Party become "unpersons", disappearing with all evidence of their existence destroyed.
In London, Winston Smith is a member of the Outer Party, working at the Ministry of Truth, where he rewrites historical records to conform to the state's ever-changing version of history. Winston revises past editions of The Times, while the original documents are destroyed after being dropped into ducts leading to the memory hole. 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. In a lunch conversation with his co-worker Syme, who is assisting in developing a revised version of Newspeak (a controlled language of limited vocabulary), Syme bluntly reveals the true purpose of Newspeak: to reduce the capacity of human thought. Winston reflects that Syme will disappear as he is "too intelligent" and therefore dangerous to the Party. Winston also discusses preparations for Hate Week with his neighbour and colleague Parsons.
One day, Julia secretly hands Winston a note saying she loves him, and the two begin a torrid affair; an act of rebellion as the Party insists that sex is only for reproduction. Julia shares Winston's loathing of the Party, but he realizes that she is politically apathetic and uninterested in overthrowing the regime, thinking it impossible. Initially meeting in the country, they 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 tense 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 is recalled to the Ministry to help make the major necessary revisions of the records. Afterwards 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 is motivated to maintain power.
Winston and Julia are captured and imprisoned when Mr. Charrington is revealed to be a Thought Police agent. At the Ministry of Love, Winston briefly interacts with colleagues who have been arrested for other offences. O'Brien arrives, revealing himself as a Thought Police agent, who tells Winston that he will never know whether the Brotherhood actually exists and that Emmanuel Goldstein's book was written collaboratively by O'Brien and (presumably) other Party members. Over several months, Winston is starved and tortured 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 the party's invincibility and its principles. Winston accepts internally that he really means he has not rescinded his feelings toward Julia; he betrays her by revealing her crimes many times. 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 takes Winston to Room 101 for the final stage of re-education, which contains each prisoner's worst fear, indicating that the level of surveillance on the public is far more thorough than initially believed by Winston. Confronted with a wire cage holding frenzied rats, his biggest fear, in his face, Winston willingly betrays Julia by wishing the suffering upon her instead. Winston is released back into public life and continues to frequent the Chestnut Tree Café. One day, Winston encounters Julia, who was also tortured. Both reveal that they have betrayed the other and no longer possess feelings for one other. Back in the café, a news alert sounds and celebrates Oceania's supposed massive victory over Eurasian armies in Africa. Winston finally accepts that he loves Big Brother.