Pongo the Dalmatian lives in a London bachelor flat with his owner Roger Radcliffe, a songwriter. Bored with bachelor life, Pongo decides to find a wife for Roger and a mate for himself. While watching various female dog-human pairs out the window, he spots the perfect couple, a woman named Anita and her female Dalmatian, Perdita. He quickly gets Roger out of the house and drags him through the park to arrange a meeting. Pongo accidentally causes both Roger and Anita to fall into a pond, but it works out well as the couple falls in love. Both the human couple and the dog couple marry.
Later, Perdita gives birth to 15 puppies. One almost dies, but Roger is able to revive it by rubbing it vigorously in a towel. That same night, they are visited by Cruella De Vil, an wealthy former schoolmate of Anita's. She offers to buy the entire litter of puppies for a large sum, but Roger says they are not selling any of the puppies. Weeks later, she hires Jasper and Horace Badun to steal all of the puppies. When Scotland Yard is unable to prove she stole them or find the puppies, Pongo and Perdita use the "Twilight Bark", normally a canine gossip line, to ask for help from the other dogs in England.
Colonel, an old Sheepdog, and Sergeant Tibbs, a tabby cat, find the puppies in a place called Hell Hall, along with lots of other Dalmatian puppies who Cruella had purchased from various dog stores. Tibbs learns the puppies are going to be made into dog-skin fur coats and the Colonel quickly sends word back to London. Pongo and Perdita quickly make their way from London to retrieve their puppies. They arrive just as Horace and Jasper are about to kill the puppies. While the adult dogs attack the two men, Colonel and Tibbs guide them from the house.
After a happy reunion with their own puppies, the Pongos realize there are 84 other puppies with them. Horrified at Cruella's plans, they decide to adopt all of the puppies, certain their pets would never reject them. The dogs being making their way back to London, aided by other animals along the way, with Cruella and the Baduns chasing behind them. In one town, they cover themselves with soot so they appear to be Labrador Retrievers, then pile inside a moving van going back to London. As the van is leaving, melting snow clears off the soot and Cruella spots them. She follows the van in her car and rams it, but the Baduns, trying to cut off the van from above, end up colliding with her, knocking both vehicles into a deep ravine. Cruella yells in frustration as the van drives away.
Back in London, Roger and Anita are attempting to celebrate Christmas and Roger's first big hit, a song about Cruella, but they miss their friends. Suddenly barking is heard outside and after their nanny opens the door, the house is filled with dog. After wiping away more of the soot, the couple is delighted to realize their companions have returned home. They decide to use the money from the song to buy a large house in the country so they can keep all 101 Dalmatians.