In the English countryside is the Manor Farm, owned by Mr. Jones, a notorious drunkard who neglects and abuses the animals under his care. One night, Mr. Jones neglects to secure his barn before retiring to bed, allowing the animals of the farm to convene a meeting. The leader among the farm animals, a large and elderly pig named Old Major, declares humanity to be the enemy of all animalkind; man uses animals as slave labor, reaping the rewards of their labor while offering nothing in return and forcing them to live in horrid conditions. He builds solidarity among the other animals by leading them in singing "Beasts of England".
A few days later, Old Major passes away. Two pigs who seemed to take Old Major's message to heart, Snowball and Napoleon, decide to use those teaching to lead the animals of Manor Farm in revolution. Under their leadership, the animals revolt against Mr. Jones and chase him out, winning their independence.
Free of man's tyranny, Manor Farm is rechristened "Animal Farm". Together, Snowball and Napoleon create a code of conduct called the Seven Commandments of Animalism. The pigs, who taught themselves how to read and write, jot the Commandments down on a board for all to see:
- "Whatever goes upon two legs is an enemy."
- "Whatever goes upon four legs, or has wings, is a friend."
- "No animal shall wear clothes."
- "No animal shall sleep in a bed."
- "No animal shall drink alcohol."
- "No animal shall kill any other animal."
- "All animals are equal."
Under the pigs leadership, Animal Farm begins to thrive. Food is plentiful and all of the animals are well fed, although the pigs take to rationing slightly more food for themselves under the pretense of maintaining their health. Snowball teaches the other animals to read and write, while Napoleon instills the teachings of Animalism into young puppies. All the while, another pig, Squealer, quiets any feelings of dissatisfaction with clever lies and propaganda.
As word of Animal Farm's prosperity spreads, other farmers band together to try and conquer the farm for themselves. The animals band together to repel the humans successfully, suffering minimal losses to their own numbers. They take Mr. Jones's gun as a trophy, which the animals agree to fire twice each year; once in celebration of the animals' successful revolution and the founding of Animal Farm, and once in celebration of their victory at the "Battle of the Cowshed".
Eventually, both Snowball and Napoleon begin to jockey with one another for the hearts and minds of the other animals. Snowball proves to be more popular, owed to his being better-spoken, his including the other animals in his discussions, and his own heroic deeds during the Battle of the Cowshed. By studying some of Mr. Jones's old books, he conceptualizes a plan to build a windmill: even though the construction of a windmill would be a long and arduous task, once it was built, it could provide electricity for the farm, automating labor and making life for the animals much easier. Napoleon disapproves of the plan, reasoning that the animals should focus on present tasks instead of lofty futurist ideas.
Nonetheless, the idea of building the windmill gains traction. As Snowball finalizes the plans for constructing the windmill, however, Napoleon sics the dogs that he had raised since puppyhood to be loyal to him upon Snowball, chasing him out of the farm. With Napoleon now the sole leader of Animal Farm, he decrees that all decision-making for the farm would fall to the pigs alone. Squealer brands Snowball as a traitor to Animal Farm, and in time, the animals come to accept Napoleon's revisions of their history in regards to Snowball, as well as the idea that Napoleon was the one who conceptualized the windmill in the first place.
The animals eventually begin construction of the windmill as Napoleon continues to allocate food for himself and the pigs at the others' expense. As the animals face difficulties in constructing the windmill due to a lack of key building materials and tools, Napoleon makes contact with a human contractor to procure construction supplies, shocking the animals until Squealer explains that the laws of Animalism never explicitly prohibited engaging in commerce with humans, and any such ideas to the contrary were lies perpetuated by Snowball. At the same time, the pigs take to sleeping in the farmhouse on beds, in violation of the Seven Commandments. In truth, the commandment had been changed to read: "No animal shall sleep in a bed with sheets".
After a particularly fearsome storm, the half-built windmill is destroyed. To quell dissent, Napoleon claims that the windmill had been sabotaged by Snowball and offers a bounty for his head as the animals are forced to begin construction of the windmill from scratch. With each passing day, Snowball becomes a greater scapegoat, blamed for many of the ills that befall the farm as Napoleon revises history to paint Snowball as a turncoat who sided with the humans during the Battle of the Cowshed, while Napoleon was the real hero who led the animals to victory that fateful day. To crush any idea of animals siding with Snowball, Napoleon stages an inquisition and purge during which he has several animals killed for supposedly being in league with Snowball, as well as declaring that "Beasts of England" may no longer be sung; it was meant for the revolution, which had come and gone, and is now replaced with a new anthem singing the praises of Animal Farm.
In response to Napoleon's purge, another of the Seven Commandments is amended: "No animal shall kill any other animal without cause."
Life under Napoleon is hard and arduous as food runs short, but the animals continue to labor on building the windmill, reasoning that they were no worse off than when they suffered under Mr. Jones.
The construction of the windmill finally comes to its completion, but following acts of deception from humans, the farm comes under siege by humans once more. This time, the humans employ dynamite to destroy the windmill and armed men to fight against the animals. Once more, the animals emerge victorious, but at great cost; several animals are killed and wounded. Among those injured in the fighting is Boxer, an old workhorse who exemplified the ideals of Animal Farm by working as hard as he could and giving everything and more to the farm.
As the pigs discover the joys of drinking liquor and amend yet another Commandment, "No animal shall drink alcohol to excess", Boxer continues to work hard in spite of his injuries to rebuild the windmill. Eventually, however, Boxer's strength fails him and he collapses, unable to stand again. The pigs call a veterinarian to take Boxer to an animal hospital. A taciturn donkey named Benjamin, however, realizes that Boxer is not being taken to a vet; being as well-read as the pigs, he is able to read the sign on the truck that came to take Boxer to a glue factory. The other animals stage a desperate rescue attempt, but to no avail. Squealer explains that the van had been recently bought by an animal hospital and had not yet painted over the glue factory markings, and that he had been with Boxer during his final moments at the animal hospital, an explanation the other animals accept at face value.
Many years pass. Most of the animals that took part in overthrowing Mr. Jones have died, and few remember the days before the revolution. The windmill is finally completed, but rather than provide electricity for the farm, it is only used to grind corn. The pigs and dogs live in comfort while the rest of the farm continues to live in dismal conditions, in spite of the farm's prosperity. In time, the pigs fully embrace the lifestyle of man; wearing clothes and walking on two legs. The consolidation of their power is completed with the Seven Commandments of the farm condensed to only one commandment:
"All animals are equal, but some animals are more equal than others."
The pigs eventually enter into talks with the local farmers about an alliance, during which the farmers praise Napoleon for getting the animals he reigns over to work more for less food as Napoleon declares that his animals would no longer speak of Old Major, no longer engage in the ceremonial customs they had in the days following the revolution, and would revert the name of Animal Farm back to "The Manor Farm". During a game of cards, however, a brawl breaks out between the pigs and the farmers as the animals watching them come to the sobering conclusion that they could no longer tell the difference between man or pig...
