A prize-winning boar named Major has a dream that he shares with the other animals of Manor Farm one night after the drunken farmer who owns the farm, Mr. Jones, has fallen asleep. Major advises the animals to reject misery and slavery and to rebel against Man, “the only real enemy we have.” The rebellion, on Midsummer’s Eve, drives Mr. Jones and his men off the farm.
Major draws up Seven Commandments of Animalism to govern the newly named Animal Farm, stipulating that “whoever goes on two legs is our enemy,” that “all animals are equal,” and that they shall not wear clothes, sleep in beds, drink alcohol, or kill any other animal. The pigs quickly assume a supervisory position to run the farm, and two of them, Snowball and Napoleon, become leaders after the death of old Major. Factions develop, and Napoleon conspires against Snowball after the animals defeat an attempt by Mr. Jones and the neighboring farmers to recover the farm at the Battle of the Cowshed.
Snowball is a brilliant debater and a visionary who wants to modernize the farm by building a windmill that will provide electrification. Two parties are formed, supporting “Snowball and the three-day week” and “Napoleon and the full manger.” Meanwhile, the pigs reserve special privileges for themselves, such as consuming milk and apples that are not shared with the others.
Napoleon raises nine pups to become his guard dogs. After they have grown, his “palace guard” drives Snowball into exile, clearing the way for Napoleon’s dictatorship. Napoleon simplifies the Seven Commandments into one slogan: “Four legs good, two legs bad.” With the help of Squealer, his propagandist, Napoleon discredits Snowball’s bravery and leadership in the Battle of the Cowshed and claims as his own the scheme to build a windmill. Every subsequent misfortune is then blamed on Snowball.
Thereafter, the animals work like slaves, with Napoleon as the tyrant in charge. Gradually the pigs take on more human traits and move into the farmhouse. Before long, they begin sleeping in beds and consuming alcohol. Napoleon organizes a purge, sets his dogs on four dissenting pigs who question his command, and has them bear false witness against the absent Snowball. He then has the dogs kill them, violating one of the Seven Commandments, which are slyly emended to cover the contingencies of Napoleon’s rule and his desires for creature comforts.
Eventually, Napoleon enters into a political pact with one neighboring farmer, Pilkington, against the other, Frederick, whose men invade Animal Farm with guns and blow up the windmill. Working to rebuild the windmill, the brave workhorse Boxer collapses. He is sent heartlessly to the glue factory by Napoleon, who could have allowed Boxer simply to retire. All the principles of the rebellion eventually are corrupted and overturned. Finally, the pigs begin to walk on their hind legs, and all the Seven Commandments ultimately are reduced to a single one: “All Animals Are Equal, but Some Animals Are More Equal Than Others.” The pigs become indistinguishable from the men who own the neighboring farms, and the animals are no better off than they were under human control.