Chanel, a wire-haired dachshund, died at her owners' home in Port Jefferson Station on Long Island, N.Y.
She was just six-weeks-old when Denice and Karl Shaughnessy adopted her from a shelter.
They nominated her for the title of world's oldest dog after noticing the Guinness World Records book was lacking the record.
The pooch was presented with a certificate at a birthday bash earlier this year, which took place a dog hotel and spa in Manhattan, complete with a peanut butter cake made especially for dogs.
"She once ate an entire bag of Reese's peanut butter cups, and, you see, she lived to be 21, so go figure," Denice Shaughnessy said.
But Chanel's owners put her long life down to more than just her daily exercise and home-cooked chicken meals.
"Dogs are God's angels sent here to look out for us," Shaughnessy said.