Aysgarth, North Yorkshire born goalkeeper Harry Walker began his football career with Leyburn in 1933 and joined Third Division (North) Darlington in December 1934, initially as understudy to Jack Beby, making his Football League debut against Mansfield Town in January 1936. When Beby departed to Exeter City, he found himself sharing goalkeeping duties with Ken Parkinson, until he was signed by First Division Portsmouth in March 1938 after 57 appearances for The Quakers, soon taking over the goalkeeping gloves from Jimmy Strong. In his first full season at Fratton Park he was part of the team that made it all the way to the 1939 FA Cup Final, where they surprisingly beat favourites Wolverhampton Wanderers in the Final at Wembley by four goals to one.
His Portsmouth career was significantly interrupted by the Second World War, but after the War he returned to Fratton Park, and although no longer their regular goalkeeper, Ernie Butler having taken over as the incumbent, he made 13 further appearances to take his total appearances for Pompey to 60, before being signed by Second Division Nottingham Forest in April 1947. Although they were relegated in 1949, they won the Third Division (South) Championship in 1951, with Walker an ever present, and he missed very few matches for 7 seasons under manager Billy Walker before losing his place in October 1954. He played once more for Forest in February 1955 before retiring at the end of the 1954-55 season, already aged 39, after 304 appearances for The Reds.