The decision was welcomed by his manager, Tommy Wright, who rates the 31-year-old goalkeeper highly.
Mannus, who defied club physios to return early from a broken thumb in last week's loss to Celtic, revealed he had been made to feel at home in Perth, and also in the middle of charge towards a top-six league finish and a possible William Hill Scottish Cup triumph.
"I am very happy to be signing on for another year," said Mannus. "I feel welcome and wanted and that made up my mind for me.
"I would still love to give it a go in England. I have never tried it and it would be nice to see what I could do, but I have a good thing here."