William Cox is a British-Australian composer and countertenor. His works span a wide range, from expansive pieces for large ensembles such as It Rests Untarnished (premiered by Jac van Steen and the BBC National Orchestra of Wales in 2025) down to the more intimate Wither Thou Goest (premiered in New College Chapel by Erika Baikoff and Dónal McCann in 2024). In June 2025, he was awarded The Paul Mealor Award by the Welsh Music Guild.

As a soundtrack composer William is attached to the upcoming feature film The Reformation of Sister Edith, starring Dominic West and Tara Fitzgerald, from production company, Intake Films (The Brutalist), and has composed for several theatre shows where his work has been described as 'incredibly clear' and 'excellently crafted'.

Since the summer of 2024, William has been composer-in-residence for the vocal octet Contrepoint, and as such has written for some of the best singers of his generation and has had work performed in many of the UK's most prestigious venues. He is currently busy writing for their upcoming tour of Belgium and performance in Guildford Cathedral.