McAllister started his working life packing chickens, then spent two years as a clerk in the Ministry of Defence in Bath while contributing cartoons to the local paper. Leaving the civil service for a graphics course at the Royal West of England College of Art, he became daily topical cartoonist for the WesternDaily Press while still a student. He then worked for the London Press Exchange advertising agency, as a copywriter for clients such as Cadbury's and Beecham's, before leaving to join a TV production company. He then joined Vernon's advertising agency, where he was a writer and producer, and also drew a strip for TV Times about two philosophical tramps whose only possession was a TV set. McAllister was best known for his Guardian pocket cartoons, which were published in the paper from 1974 until the radical redesign of the Guardian in 1989. In 1990 he returned to the Guardian with an occasional feature of words and drawings called "McAllister's Eye", and in 1996, after the merger of the Guardian and the Observer, he also began contributing pocket cartoons to the Observer.