William Kostakis undertook his secondary education at Newington College, Sydney. He then went on to undertake a Bachelor of Arts (Media and Communications) at Sydney University.
He published his first novel when he was nineteen; he had previously won Sydney Morning Herald's Young Writer of the Year for a collection of short stories, while still in high school.
His second novel was shortlisted for the Prime Minister's Literary Award, among other wins and shortlists. His third novel also marked his debut in the American market, it won the Ena Noël Award (IBBY Awards) and was a finalist for the international Lambda Awards.