Ecclesall, Yorkshire born inside right Jack Blackwell began his football career with Chapel-en-le-Frith in neighbouring Derbyshire, from where he was signed by First Division club Huddersfield Town in October 1931, making his Football League debut against Arsenal towards the end of April 1932, playing once more before the season end in a defeat at Blackpool as The Terriers finished fourth in the League Championship. Blackwell featured once more for Huddersfield in a 4-0 win over Newcastle United before signing for Second Division club Charlton Athletic in October 1932, where he played in most of their remaining fixtures between his debut at Swansea Town at the end of October and the end of the season, as Charlton were relegated at the end of the season despite Blackwell contributing 6 goals to their campaign.
He struggled to gain a regular place the following season before being signed by Second Division club Port Vale in February 1934 after 8 goals in 40 appearances for The Addicks. He scored a brace on his debut in a 5-1 win over Millwall at The Old Recreation Ground on 24th February, and stayed for a further full season with The Valiants, but lost his place after suffering a serious knee injury in August 1934, , which sidelined him for four months. He moved to Midland League club Boston Town in the summer of 1935 for a season after scoring 5 goals in 25 matches for Port Vale, then joined Southern League club Ipswich Town for their penultimate season as a non league club, scoring 15 goals in 28 matches across all competitions, he helped The Tractor Boys to win the 1936-37 Southern League Championship. after which he returned to Yorkshire, joining Bridlington Town in 1937, his final club before his eventual retirement.