The book begins with the animals of Manor Farm, led by the wise old boar named Old Major, who shares his dream of a utopian society free from the exploitation and oppression of humans. Inspired by Old Major's vision, the animals rise up against their human owner, Mr. Jones, and take control of the farm, renaming it "Animal Farm."
At first, Animal Farm thrives under the principles of Animalism, a set of commandments formulated by the pigs, Snowball and Napoleon, who become the leaders of the newly formed animal republic. The animals work together to cultivate the land, and all decisions are made through a democratic process in the form of meetings called by the pigs.
However, as time passes, the pigs gradually assume more power and privileges. They revise the commandments to suit their own interests and establish themselves as the ruling class. Snowball, a visionary and eloquent speaker, is eventually driven off the farm by Napoleon, who seizes complete control and becomes a dictator.
Under Napoleon's leadership, the farm undergoes significant changes. The pigs exploit the other animals, monopolise resources, and manipulate the commandments to justify their actions. They engage in propaganda and employ a terrifying enforcer, the dogs, to suppress dissent and maintain control. Despite the worsening conditions and broken promises, the animals, especially the loyal and hardworking horse named Boxer, remain dedicated to the cause, convinced that they are building a better society.
As time goes on, the pigs become indistinguishable from the humans they once rebelled against. They walk on two legs, wear clothes, and even socialise with humans. The original principles of Animalism are forgotten, and the pigs rewrite history to suit their narrative. The book's famous mantra, "All animals are equal, but some animals are more equal than others," encapsulates the pigs' hypocrisy and corruption.
In the end, the animals realise that they have become oppressed by their own leaders, but it is too late to reverse the course. They witness the pigs collaborating with humans, symbolising the betrayal of the revolution's ideals. The story concludes with the animals watching the pigs and humans during a meeting and finding it impossible to distinguish between the two.