Bobi is a purebred Rafeiro do Alentejo - a breed that has an average life expectancy of 12 to 14 years.
BBC reports the news comes just two weeks after Spike the Chihuahua, 23, was given the record for the oldest living dog.
The previous oldest dog ever was Australia's Bluey, who died in 1939 at the age of 29 years and five months.
As of 1 February, Bobi was 30 years and 226 days old.
This has been validated by the Portuguese government's pet database, which is managed by the National Union of Veterinarians, according to Guinness World Records.
He has lived his whole life with the Costa family in the village of Conqueiros, near Portugal's west coast, after being born with three siblings in an outbuilding.
Leonel Costa, who was eight years old at the time, said his parents had too many animals and had to put the puppies down, but Bobi escaped.
Leonel and his brothers kept the dog's existence a secret from their parents until he was eventually discovered and became part of the family, who feed him the same food they eat.
"Between a can of animal food or a piece of meat, Bobi doesn't hesitate and chooses our food," said Costa, who always soaks the food in water to remove most of the seasoning.
Apart from a scare in 2018 when he was hospitalised after suddenly collapsing due to breathing difficulty, Costa says Bobi has enjoyed a relatively trouble-free life and believes the secret to his longevity is the "calm, peaceful environment" he lives in.
It may also be in the blood - Bobi's mother living to the age of 18.
However, time has taken its toll on Bobi, who now has trouble walking and worsening eyesight.
Costa says Bobi is the "last of a long generation of animals" in the Costa family and describes him as "one of a kind."