Knox trained as an architect at Edinburgh College of Art (1963–67) and Heriot-Watt University (1967-68), and worked as an architect before establishing himself as a cartoonist. He worked in animation from 1970 to 1975 for Halas & Batchelor in London, Potterton Productions in Montreal, and Kotopoulis Productions in Toronto. He then joined Red Weekly and Socialist Challenge as a political cartoonist, as well as contributing to various children's comics for IPC from 1975-80.
He signed much of his political work "Blotski", and he and Republican News cartoonist Cormac worked together as "Kormski", drawing the anti-clerical strip "Dog Collars" for Fortnight Magazine. Since 1989 he has been the editorial cartoonist for The Irish News.