Midfielder Mason progressed through the ranks at White Hart Lane and made over 50 Premier League appearances under Mauricio Pochettino but was apparently made surplus to requirements for the coming season after the signing of Victor Wanyama.
Hull started their season with wins in their first two games against Leicester City and Swansea City, despite caretaker manager Mike Phelan having just 13 senior players available.
United striker Will Keane and Wales' Euro 2016 hero Hal Robson-Kanu have also been linked with the KCOM Stadium.
After Hull struck a deal reportedly in the region of £10million to sign Mason, he told the club's official website: "I'm delighted and excited to be here.
"I can't wait to get started and I see this as a massive opportunity for me."
Mason had also been linked with a move to Sunderland, but confirmed to Sky Sports News that he rejected a move to Wearside on "gut feeling".