In the year 1984, civilization has been damaged by war, civil conflict, and revolution. Airstrip One (formerly 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" and the mysterious leader Big Brother, who has an intense cult of personality. The Party stamps out 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. He works 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 by fire in a "memory hole". He secretly opposes the Party's rule and dreams of rebellion. He realizes that he is already a "thoughtcriminal" and likely to be caught one day.
While in a proletarian neighbourhood, he meets Mr. Charrington, the owner of an antiques shop, and buys a diary. He uses an alcove to hide it from the Telescreen in his room, and writes thoughts criticising the Party and Big Brother. In the journal, he records his sexual frustration over a young woman maintaining the novel-writing machines at the ministry named Julia, whom Winston is attracted to but suspects is an informant. He also suspects that his superior, an Inner Party official named O'Brien, is a secret agent for an enigmatic underground resistance movement known as the Brotherhood, a group formed by Big Brother's reviled political rival Emmanuel Goldstein.
The next day, Julia secretly hands Winston a note confessing her love for him, which simply reads, "I love you." Winston and Julia begin a torrid affair, an act of the rebellion as the Party insists that sex may only be used for reproduction. Winston realizes that she shares his loathing of the Party. They first meet in the country, and later 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 ex-wife Katharine. Winston also interacts with his colleague Syme, who is writing a dictionary for a revised version of the English language called Newspeak. After Syme admits that the true purpose of Newspeak is to reduce the capacity of human thought, Winston speculates that Syme will disappear. Not long after, Syme disappears and no one acknowledges his absence.
Weeks later, Winston is approached by O'Brien, who offers Winston a chance to join the Brotherhood. They arrange a meeting at O'Brien's luxurious flat where both Winston and Julia swear allegiance to the Brotherhood. He sends Winston a copy of The Theory and Practice of Oligarchical Collectivism by Emmanuel Goldstein. 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" (proletarians) rise up against it.
Mr. Charrington is revealed to be an agent of the Thought Police. Winston and Julia are captured in the shop and imprisoned in the Ministry of Love. O'Brien reveals that he is actually loyal to the Party, and was simply part of a special sting operation to catch "thoughtcriminals". Over many months, Winston is tortured and forced to "cure" himself of his "insanity" by changing his own perception to fit the Party line, even if it requires believing that "2 + 2 = 5". O'Brien openly admits that the Party "is not interested in the good of others; it is interested solely in power." He says that once Winston is brainwashed into loyalty, he will be released back into society for a period of time, before they execute him. Winston points out that the Party has not managed to make him betray Julia.
O'Brien then takes Winston to Room 101 for the final stage of re-education. The room contains each prisoner's worst fear, in Winston's case rats. As a wire cage holding hungry rats is fitted onto his face, Winston shouts "Do it to Julia!", thus betraying her. After being released, Winston meets Julia in a park. She says that she was also tortured, and both reveal betraying the other. Later, Winston sits alone in a café as Oceania celebrates a supposed victory over Eurasian armies in Africa, and realizes that "He loved Big Brother."