Dennis started his career in the academy of Luton Town before moving to join the Watford academy, where he played from under-9s up to under-16s.[2] After being released by Watford, Dennis had trials with Milton Keynes Dons, Coventry City and Stevenage.[2]
Dennis joined AFC Bournemouth at the age of 15 in 2016, turning professional 18 months later and joining the first-team at the start of the 2019–20 season.[3] He also had spells in non-league with Guernsey and Weymouth during the 2017–18 season.[4]
In March 2020 he signed a new three-and-a-half-year contract with the club.[5][6] Later that month he was praised by manager Eddie Howe.[7]
On 11 December 2021, Dennis signed for Wealdstone on an emergency loan.[8] He made his debut on the same day, in a 1–0 defeat to Halifax[9] On 18 December 2021, Dennis was recalled from his loan spell by parent club Bournemouth.[10]