Oakley, an overweight golden retriever, has shed a stone (7.6kg) to become a charity's slimmer of the year.
Oakley liked to curl up in front of the TV with a packet of Rich Tea
The six-year-old from Plymouth piled on the pounds thanks to a love of Rich Tea biscuits, but won the competition after shedding nearly a fifth of his weight.
He has swapped his sedentary routine for a lifestyle of long walks and playing in the park.
He beat five other pets to be crowned the People's Dispensary for Sick Animals' (PDSA) fitness champ.
When Oakley began his slimming challenge in September he weighed in at a hefty 7st 4lb (46.5kg).
His efforts mean he has won a two-day holiday in Dorset for himself and owner Lisa Deadman.
She said: "I'm so proud of Oakley and the slimming success he has achieved in such a short time.
"We used to enjoy cuddling up in front of the TV and snacking on our favourite biscuits, but that has all changed.
"Oakley has so much more energy now he is slimmer, and we enjoy going for long walks and playing in the park instead."
In second place was Buster, a six-year-old Staffordshire bull terrier from London who shed 7lb (3.2kg), 13% of his body weight, thanks to an exercise programme.
Third was one-time fat cat Pebbles, five, also from London, who shifted 1.5lb (0.65kg), 8.7% of her weight, by curbing her love of fatty foods and stealing nibbles from other cats.
Elaine Pendlebury, PDSA senior veterinary surgeon, said: "Many of these pets have discovered a new lease of life after losing their excess weight.
"Eating more healthily and taking regular exercise, as recommended by your vet, may well improve a pet's overall enjoyment of life."