John Fitter, who fought the election as an Independent, congratulated Glanville and said this would probably be the end of his political career.
Fitter had been attempting to regain the seat he lost to Reform UK in May – which brought an end his 16-year spell on the council.
“I think this is the end for me. I’ve been very lucky and privileged to serve the people of my division,” he said.
“I really thank them very much indeed for their loyalty to me. I really believe that they will be well served by their new Cornwall councillor.”
Councillor Leigh Frost, the Liberal Democrat leader of the council, said the party would “continue to keep fighting to improve Cornwall”.
“Of all the parties that stood in May’s elections we’re the only one to see a huge increase in vote share,” he said.