TobyKeith lives in Florida with his owner Gisela Shore, who adopted him from a shelter when he was only a few months old.
Speaking to the Guinness World Records, Shore said she "began to suspect" he was closing in on the record shortly after his 20th birthday.
"I was a volunteer at Peggy Adams Animal Rescue, and one of the employees told me about an elderly couple trying to surrender a puppy because they could not take care of him any longer," she said.
"I met with the elderly couple, and I was introduced to a tiny tan chihuahua. They had named him Peanut Butter. I later changed his name to TobyKeith."
Shore added, "people can't believe how good he looks for his age", a feat considering chihuahuas typically live between 12 and 18 years.
The record for the oldest ever dog recorded belongs to an Australian cattle dog named Bluey. He lived to the impressive age of 29 years and five months in 1939.