Born in Camberwell, Harry Wallis was the middle of three brothers who all played for the Dons. He served in the army during the Second World War before joining the Dons in 1947 and spending three seasons in the Strollers (third team). He became part of the first team after making his début in a London Senior Cup tie against Hayes in March 1950 and quickly made the centre half position his own.

Much quieter than either of his other brothers, he remained part of the team until the autumn of 1957 when he left plough lane for good following a dispute over the payment of players.

Won representative honours with the Surrey, Isthmian and F.A. sides and was at one point tipped for international honours.

He moved to Bromley and continued to make regular appearances at Plough Lane over the next few seasons. Away from football he was a ballet shoe maker.