[2] He played football for Hylton Colliery Juniors and for the Durham youth side[3] before joining West Ham United in November 1950 when his father, also named Harry Hooper, was appointed assistant trainer at the club.

[2][4] He played for the reserve team in the London Combination before making his debut in the Football League on 3 February 1951, at the age of 17 years 7 months, at home to Barnsley in the Second Division.

West Ham won 4–2, and Hooper himself came close to scoring eight minutes from time, when "Barnsley's Pat Kelly had to stretch like elastic to push Harry's 25-yard drive over the bar".

[5][6] The 1954–55 season saw Hooper make 41 league appearances for West Ham, one short of being an ever-present.

[15] He then joined Birmingham City for a fee of around £20,000, spending nearly three years at the club and winning a runners-up medal in the 1960 Fairs Cup.