[1] He began his career at Ayr United, coming through the academy and making 245 appearances for The Honest Men.
He is the younger brother of Celtic and Scotland winger James Forrest;[2] their sister Lisa is also a footballer.
[3][4] Forrest made his debut for Ayr United in a Scottish Challenge Cup match against Queen's Park.
With this goal Forrest became Ayr's youngest ever goalscorer aged 16 years, 321 days.
He scored his first goal for Livingston in a 2–2 draw against Motherwell on 12 August 2020, at Fir Park.