Sheffield born goalkeeper Harry Blackwell began his football career with Heeley Friends in 1919 before joining Midland League Scunthorpe & Lindsey United in 1920. In September 1921 he moved to Aberdeen, making his Scottish League debut the same month in a 1-1 draw at Clydebank. He played less than half the games in his debut season before establishing himself, remaining ever present for the following two seasons and missing only 3 games in the next two. He kept goal when Aberdeen recorded their record 13-0 victory against Peterhead and purportedly sheltered under an umbrella and wore an overcoat while watching proceedings!
He made 252 appearances for Aberdeen before heading south to join Third Division (South) Clapton Orient in July 1930, making his Football League debut at Walsall that August. However he only made 16 appearances during the next two seasons, and in July 1932 he joined Preston North End where he was understudy to Harry Holdcroft, not making a first team appearance before he then returned to Scotland to join Forfar Athletic in July 1933 for a season, finishing his career in May 1934.
His older brother Ernest Blackwell was also a goalkeeper who played for Scunthorpe & Lindsey United and Sheffield United both sides of the First World War. Perhaps the most famous goalkeeper of the era, Sam Hardy, was a cousin.