Born in Birmingham, Peter Maddocks attended the Moseley School of Art and served in the Merchant Navy from 1943 to 1949. He then became a letterer with the Amalgamated Press and set up his own advertising agency in London. In the 1950s, he became a cartoonist for the Daily Sketch and the Daily Express.
For the latter, he made the popular comic strip 'Four-D Jones' that ran until 1965. Another strip by Maddocks was 'Horatio Cringe' for the Glasgow Evening Citizen. In the 1960s, he worked as a sport and pocket cartoonist for the London Evening Standard and he began a long collaboration with Mayfair magazine.
Maddocks drew the strip titled 'No. 10' for the Sunday Express from 1970, as well as the animal strip 'A Leg At Each Corner' in the Manchester Evening News. His 'Slightly Maddocks' cartoons appeared in the London Evening News and the took over 'Useless Eustace' from Jack Greenall in the Daily Mirror. Maddocks wrote several books on cartooning, like 'How to be a Super Cartoonist' and 'Caricature and the Cartoonist'. His animated films for the BBC include 'The Family-Ness' (1983), 'Jimbo and the Jet Set' (1986) and 'Penny Crayon' (1990).