Bobi, a purebred Rafeiro Alentejano that spent all of his life in a village in central Portugal lived for 31 years and 165 days and broke the previous record of 29 years and 5 months held by an Australian cow dog.
Bobi's death was confirmed by Guinness World Records.
"Despite outliving every dog in history, his 11,478 days on earth would never be enough for those who loved him," said Karen Becker, a veterinarian who met Bobi several times and who was the first to announce his death on social media. "Godspeed, Bobi."
In February of this year, he was recognised as the oldest dog in the world.
The typical lifespan of Bobi's breed, which has historically been used as sheepdogs, is 12 to 14 years.
Leonel Costa, his owner, gave a multitude of explanations for his long life, including living in peace in the country, never being tied or kept on a leash, and always eating "human food."
Costa's family had many animals and little money at the time Bobi was born, so his hunter father typically buried newborn puppies rather than keeping them.
However, Bobi hid among some firewood. A few days later, Costa and his brothers discovered him and kept him hidden until the puppy opened his eyes.
"We knew that when he opened his eyes, my parents wouldn't be able to bury him," Costa told Reuters earlier this year.
Bobi still enjoyed going for walks, but he was less daring before he passed away. He needed more rest than usual because his fur was thinning, his eyesight had gotten weaker, and so on.
Bobi's story has previously been referred to as "miraculous" by Guinness World Records, which also stated on Monday that "he will be sorely missed." At his 31st birthday party in May, more than 100 guests attended, it stated.