Twin brother of actor Harry Treadaway.
Treadaway was born in Exeter, Devon, England, and brought up in Sandford, near Crediton, Devon.
Treadaway attended Queen Elizabeth's Community College in Crediton.
His father is an architect and his mother is a primary school teacher.
He was awarded the Laurence Olivier Theatre Award as Best Actor, for his performance in "The Curious Incident of the Dog in the Night-Time". .
February - May 2017: appearing as "Nick" in the West End revival of Edward Albee's "Who's Afraid of Virginia Woolf" at the Harold Pinter Theatre, which also features Imelda Staunton, ("Nick") Conleth Hill ("George") and Imogen Poots ("Honey") .