[4] He began acting as a hobby when he was a child, and later taking part in an intensive at the National Youth Theatre at 16.

Clemmett's first audition was for Lord of the Flies, going on to make his professional acting debut as Bill in the 2011 production of Nigel Williams' stage adaptation at Regent's Park Open Air Theatre.

[5] He made his television debut in 2013 with guest appearances in Foyle's War on ITV and Doctors on BBC One.

[6] Clemmett went on to play Ernst in Nivelli's War at the MAC in Belfast[7] and Ian Trenting in Accolade at St James Theatre in London in 2014, and then Mark in WINK at Theatre503 and Tom in the Royal Shakespeare Company production of Wendy & Peter Pan in 2015.

He portrayed young Brimsley in the 2023 Netflix prequel Queen Charlotte: A Bridgerton Story.