In 1984, civilisation has been ravaged 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 known as memory holes, which lead to an immense furnace. He secretly opposes the Party's rule and dreams of rebellion, despite knowing that he is already a "thought-criminal" and is likely to be caught one day.
While in a prole neighbourhood he meets Mr. Charrington, the owner of an antiques shop, and buys a diary where he writes criticisms of the Party and Big Brother. To his dismay, when he visits a prole quarter he discovers they have no political consciousness. 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, 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.
One day, Julia secretly hands Winston a love note, and the two begin a secret affair. Julia explains that she also loathes the Party, but Winston observes that she is politically apathetic and uninterested in overthrowing the regime. Initially meeting in the country, they later meet in a rented room above Mr. Charrington's shop. During the affair, Winston remembers the disappearance of his family during the civil war of the 1950s and his tense relationship with his estranged wife Katharine. Weeks later, O'Brien invites Winston to his flat, where he 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, which goes mostly unnoticed. Winston is recalled to the Ministry to help make the necessary revisions to the records. Winston and Julia read parts of Goldstein's book, which explains 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, Winston never gets the opportunity to read the chapter that explains 'why' the Party is motivated to maintain power.
Winston and Julia are captured when Mr. Charrington is revealed to be a Thought Police agent, and they are imprisoned at the Ministry of Love. O'Brien arrives, also revealing himself as a Thought Police agent. O'Brien tells Winston that he will never know whether the Brotherhood actually exists and that Goldstein's book was written collaboratively by him and other Party members. Over several months, Winston is starved and tortured to bring his beliefs in line with the Party. O'Brien takes Winston to Room 101 for the final stage of re-education, which contains each prisoner's worst fear. When confronted with a cage holding frenzied rats, Winston denounces Julia to save himself, and pledges allegiance to the Party.
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 betrayed the other and are no longer in love. Back in the café, a news alert celebrates Oceania's supposed massive victory over Eurasian armies in Africa. Winston finally accepts that he loves Big Brother.