The striker came through the youth ranks at Bury, making two first team appearances in the EFL Trophy, before signing for the then Premier League side Burnley, scoring his first goal days after signing in a pre-season friendly against Stalybridge Celtic. During the 2019/20 season, Harker spent time on loan at Hartlepool United in the Vanarama National League, making seven appearances in February and March.

During the 20/21 season, Harker made 11 appearances in the Premier League 2, helping the under 23 side to a 7^th placed finish. Last season, Harker made just six appearances for the under 23s in the Premier League 2, due to an injury.