Tohby Riddle was raised in Sydney, and his early years were spent at a Steiner school. After school he became a mailing clerk at what was then Pan Books Australia. He completed a BA in Visual Arts at the Sydney College of the Arts and he studied for a degree in architecture at the University of Sydney. In 1989 Riddle began writing and illustrating picture books, which have been published in the United Kingdom and the United States as well as in Australia.
Riddle has also contributed cartoons to Good Weekend and the Sydney Morning Herald. A selection of his cartoons was published in What's the Big Idea? (Penguin Viking, 2003). Riddle's articles, illustrations and various writings have appeared in the NSW School Magazine, where he has been an occasional member of the editorial staff. He has also visited schools to talk about his work, and has expressed a belief that the picture book medium offers great opportunities for storytelling aimed at people of all ages. Riddle has also made appearances at the Sydney and Melbourne Writers' Festivals.
In 2016, his The Greatest Gatsby: A Visual Book of Grammar was shortlisted for a Prime Minister's Literary Award (Children's Fiction) and was included on the White Ravens list.