Blackwell, Derbyshire born inside forward (who played all three central positions) Harry Hill played junior football for Birdholme Rovers prior to the First World War and played for New Hucknall Colliery in 1918 before signing for First Division Notts County in May 1919, for whom he had played as a wartime guest in 1918, where he spent the first five seasons of his professional career. He made his Football League debut at Manchester City in September 1919, a season in which they were relegated to the Second Division. In 1922 he was in the Notts County team that lost to eventual winners Huddersfield Town in the FA Cup semi final at Turf Moor and the following season he scored 12 goals as they finished Second Division Champions to return to the top flight.
Second Division club Sheffield Wednesday bought him in October 1924 after 56 goals in 170 games for The Magpies and he again scored 12 goals as Wednesday won the Second Division Championship in 1926, but back in the First Division he struggled to hold down a place in their first eleven playing only 42 more matches in the next three seasons, before transferring to Midland League club Scarb0rough in the summer of 1929 after 40 goals in 99 games for The Owls.
At Scarborough he won the Midland League Championship in 1930, but he returned to Football League action with Chesterfield in the summer of 1932 as player-coach, playing 11 times and scoring twice for The Spireites, and he then spent the 1933-34 season at Mansfield Town scoring 5 goals in 25 matches for The Stags, from where he joined Midland League club Sutton Town in the 1934 close season, his final club before his eventual retirement.