William worked as a theatre director before his first short film Best won the Sundance London Short Film Competition in 2013. His debut feature film Lady Macbeth premiered at the Toronto Film Festival in 2016 and was nominated for three BAFTA awards, an Film Independent Spirit award for Best International Film and won the European Film Academy Discovery Prize. His second film Eileen, was an adaptation of Ottessa Moshfegh’s debut novel. It premiered at Sundance in 2023 and has been nominated for three Film Independent Spirit Awards including Best Director.