He will link up with Ian Goodison at Prenton Park, rekindling the Jamaican partnership they once had at Hull City. Also on the books is winger David Beresford, all three of whom have been brought to the club by Brian Little who also previously managed them at Boothferry Park.
Little said on the official Rovers website: "We have in Theo a midfield player with great creativity and an eye for a goal and he's a wonderful dribbler of the ball. "People might not associate him with skill but believe me that's his trademark. He's creative, very bright and makes things happen out of nothing. "I know he will settle here quickly and I'd like to think we might create a very firm crowd favourite."
Whitmore and Goodison played for City between 1999-2002, and are set to come up against them for the first time next season in Division Two.