Born in London, Willis joined Championship club Middlesbrough aged sixteen having been spotted by Academy scout Martin Carter playing for Independent FC.[3][4]
In July 2022, Willis signed a first professional contract having impressed for the under-23s side in his third year as a scholar.[5] On 8 November 2022, he made his senior professional debut as a substitute in a 3–0 league victory away at Blackpool.[6] He was rewarded later that same week with a new contract, keeping him at the club until 2025.[7] He was unable to fully capitalise on the opportunity however, suffering an injury in January 2023 during an under-21 fixture, ruling him out until the following February.[8]