In 1993, Sirius became the first known person ever to escape from Azkaban. After receiving an issue of the Daily Prophet from Cornelius Fudge during an inspection, he discovered that Pettigrew was indeed hiding in his Animagus form as Ron Weasley's pet rat, Scabbers. Filled with the desire for revenge, Sirius took his Animagus form and, thinned from malnourishment, was able to slip through the bars of his cell and past the Dementors. He swam across the North Sea back to the mainland and to freedom. He made his way to Little Whinging to catch a glimpse of his godson as a teenager, where his appearance startled Harry before the Knight Bus turned up. As news of Sirius muttering "he's at Hogwarts" in his sleep, and subsequently escaping, was released, the wizarding community went on high alert, believing that he planned to murder Harry in a mad attempt to bring Lord Voldemort back.
Sirius took refuge around Hogsmeade and the Forbidden Forest, where he was spotted a few times and mistaken by Harry for the Grim. He made the acquaintance of Hermione Granger's cat Crookshanks, who had recognised that Sirius was not actually a dog, and who had also recognised Peter for what he was. Crookshanks attempted to bring Peter to Sirius, but Ron was very protective of his so-called pet. Half-crazed and desperate, Sirius sneaked into Hogwarts through the old passageway from the Shrieking Shack and on one occasion slashed the Fat Lady's portrait when she refused him entrance to Gryffindor Tower on 31 October 1993, which was also the anniversary of Lily and James' death. Later, he came to view the Quidditch match between Gryffindor and Hufflepuff. During the match, he witnessed Harry's excellent flying skills, which he later commented mirrored James' skills. Eventually, he was able to enter the Gryffindor common room. He accomplished this with a list of passwords Crookshanks had stolen from Neville Longbottom and shredded Ron’s bed curtains in his search for "Scabbers". Peter was nowhere to be found since Sirius' escape had prompted him to once again fake his own death and hide. In June, Sirius caught Ron carrying Scabbers, after the rat had been discovered hiding in Rubeus Hagrid's cabin, and dragged both boy and rat through the tunnel under the Whomping Willow to the Shrieking Shack. Harry and Hermione Granger followed, the former intent on confronting Sirius about the supposed betrayal of his parents, despite the obvious differences in their ages and skill levels; Sirius' weakened state (due to being on the run) at that time led to the boy easily, and without a wand, overpowering the older wizard despite Crookshanks' attempts to aid the Animagus. Once Harry had Sirius at his mercy, Remus Lupin, who had seen Peter on the confiscated Marauder's Map, disarmed Harry and warmly greeted his old friend. Together, Lupin and Sirius revealed Peter's true form. Both wanted to kill their former friend for betraying James and Lily, but Harry prevented them from doing so, believing that it would be better to force Pettigrew to face justice at the hands of the Dementors. That, and he did not want his father's friends to become murderers, as he did not think that would be what his father would want. Sirius was briefly re-captured by Snape, and was sentenced to the Dementor's Kiss, a fate worse than death. Miraculously, and by Albus Dumbledore's suggestion, Harry and Hermione used Hermione's Time-Turner to help Sirius escape; as Dumbledore had also hinted that "more than one innocent life" could be saved that night, they rescued the hippogriff Buckbeak from execution, thus granting Sirius a form of travel. Sirius was once again a wanted man, although alive, soul intact, and innocence known to at least certain people. Soon after his escape, he sent Harry, Ron and Hermione a letter via a tiny, hyperactive owl explaining that it was he who sent Harry the Firebolt for Christmas, and giving Harry permission, as his godfather, to go to Hogsmeade. He also apologised to Ron for the loss of his pet, asking him to accept the owl in place of "Scabbers".