In a dystopian 1984, Winston Smith endures a squalid existence in the totalitarian superstate of Oceania under the constant surveillance of the Thought Police. He resides in London, the capital city of the territory of Airstrip One, formerly England, and works in a small office cubicle at the Ministry of Truth, rewriting history as dictated by the Party and its supreme leader, Big Brother, who never appears publicly but instead appears only on propaganda posters, advertising billboards, and television monitors. He also occasionally attends public rallies at Victory Square where the citizens are shown propaganda films of the current war situation as well as contradictory and false news stories about Oceania's war effort to unite the civilized world under Big Brother's rule. While his co-worker and neighbor, Parsons, seems content to follow the state's laws, Winston, haunted by painful childhood memories and restless carnal desires, keeps a secret diary of his private thoughts, thus creating evidence of his thoughtcrime. However, he tries to do it undercover of the telescreens, to maintain his safety.

His life greatly changes when he is accosted by fellow Outer Party worker Julia, a mysterious, bold-looking, sensual, and free-spirited young woman who works as a print machine mechanic in the Ministry of Truth, and they begin an illicit affair. During their first meeting in the remote countryside, they exchange subversive ideas before having sex. Shortly after, Winston rents a room above a pawn shop in the less restrictive proletarian area where they continue their liaison. Julia procures contraband food and clothing on the black market, and for a brief few months they secretly meet and enjoy an idyllic life of relative freedom and contentment together.

Their affair comes to an end one evening, when the Thought Police suddenly raid the flat and arrest them both. It is later revealed that a telescreen hidden behind a picture on the wall in their room recorded their transgressions and that the elderly proprietor of the pawn shop, Mr. Charrington, is a covert agent of the Thought Police. Winston and Julia are taken away to the Ministry of Love to be detained, questioned and "rehabilitated" separately. There O'Brien, a high-ranking member of the Inner Party whom Winston had previously believed to be a fellow thoughtcriminal and agent of the resistance movement led by the Party's archenemy, Emmanuel Goldstein, systematically tortures him.

O'Brien instructs Winston about the state's true purpose and schools him in a kind of catechism on the principles of doublethink — the practice of holding two contradictory thoughts in the mind simultaneously. For his final rehabilitation, Winston is brought to Room 101, where O'Brien tells him he will be subjected to the "worst thing in the world", designed specifically around Smith's personal phobias. When confronted with this unbearable horror — a cage filled with wild rats — Winston's psychological resistance finally and irretrievably breaks down, and he hysterically repudiates his allegiance to Julia. Now completely subjugated and purged of any rebellious thoughts, impulses, or personal attachments, Winston is restored to physical health and released.

Winston returns to the Chestnut Tree Café, where he had previously seen the rehabilitated thoughtcriminals Jones, Aaronson and Rutherford (themselves once prominent but later disgraced members of the Inner Party) who have since been "vaporized" and rendered unpersons. While sitting at the chess table, Winston is approached by Julia, who was similarly "rehabilitated". They share a bottle of Victory Gin and impassively exchange a few words about how they have betrayed each other. After she leaves, Winston watches a broadcast of himself on the large telescreen humbly and remorsefully confessing his "crimes" against the state and imploring forgiveness from the populace.

Upon hearing a news report declaring the Oceanian army's utter rout of Eurasia's forces in North Africa, Winston, having been deprived of his freedom to think and feel for himself and reduced to a mere shell of a man, and soon to be deprived of his very physical existence as well, looks at the still image of Big Brother that appears on the telescreen, then turns away with tears in his eyes as the words "I love you" are heard whispered in his voice.