Stewart was Professor of English at the University of Adelaide 1935-1945. His first detective novel was written on his voyage to Australia and more were written while he was working in Adelaide.
Stewart was drawn into the famous Australian literary hoax, the Ern Malley affair when Max Harris, the editor of Angry Penguins and a former student of Stewart's, sought his opinion on the poems. At one stage Stewart was himself suspected of being the hoaxer and he also testified in defence of Harris when charges of obscenity were brought against him. (The detective novel From London Far mischievously alludes to the police officer involved in this prosecution.)
Stewart used the pseudonym 'Michel Innes' for his detective fiction, some of which contains Australian references and characters, but usually with an overseas setting. Stewart published other fiction and literary criticism under his own name; his quintet of novels A Staircase in Surrey, published under his own name and well after his departure from Australia, contain an important Australian character, Oxford student Martin Fish.