Winston, who is thought to be 17-years-old, was handed in at a veterinary surgery 35 miles away from his home, where vets were able to check his microchip and trace his owners.
The cat disappeared about six to eight months after Mrs Barnes moved in. At the time the couple had dogs and teenagers, which they think may have been too disruptive for Winston.
Winston was found in Launceston by some customers of Castle Veterinary Group.
Mr Barnes added: "He was in a real state when he got to the vets, they said his fur was all matted.
"Luckily Winston has a microchip so they could trace him to us. I really believe that the microchip saved his life.
"Without it, in his condition and at his age I think Winston would have faced euthanasia."
Mrs Barnes got Winston when he was only a year old.
Mr Barnes also said that their children couldn't believe that their childhood cat had returned home.
He is now settling in well, along with the couples new rescue dog.
Steve Cox, practice manager at the Castle Veterinary Group, said: "We get dogs and cats that have been separated from their owners on a regular basis, but none that have been gone for as long as Winston.
"We don't know how he managed to make the epic journey from St Austell to Launceston.
"We are urging all owners to get their animals microchipped, it's inexpensive and painless, and can help you be reunited with your lost pet."
