Forrest made his debut for Ayr United in a Scottish Challenge Cup match against Queen's Park. He came off the bench to score an 89th-minute winner at Hampden Park. With this goal Forrest became Ayr's youngest ever goalscorer aged 16 years, 321 days.[2]
On 1 June 2022, it was announced that Forrest would join Scottish Premiership side Heart of Midlothian on a two-year deal, following the expiry of his Livingston contract on 10 June.[8][9] On 19 January 2024, he signed a two-year extension to his contract until 2026.[10]