The 22-year-old started his career at Motherwell, where he was a product of their Academy.
At the start of his Fir Park career, Erwin was sent on a short loan to Arbroath, where he scored eight goals in eleven appearances for the Gayfield side.
The young Scot, who has been capped up to U19 level, made 34 appearances for the Steelmen before joining Leeds United in June 2015.
During his time at Elland Road, Erwin was sent on loan to both Bury and Oldham Athletic.
Lee made 40 appearances at Boundary Park and finished the Latics’ top goalscorer for season 2016/17.