Forbes trained at Bristol Old Vic Theatre School, graduating in 2001 as a BBC Carleton Hobbs Award winner.
[2] In 2001 he played the lead role in John Deery's debut feature Conspiracy of Silence, for which he was nominated Best Newcomer at the inaugural Irish Film and Television Awards.
He made his stage debut in Trevor Nunn's production of A Streetcar Named Desire at The Lyttelton Theatre in 2002.
From 2013 to 2016, Forbes has provided the voice of the character Connor in the CGI version of the iconic British TV series Thomas and Friends.
In 2015 he starred opposite Sharon Horgan and American comedian Rob Delaney in Catastrophe, a six-part comedy series for Channel 4[3][4] which first aired in the UK on 19 January 2015.