John Peter Michael Donegan was born in Lewisham, London on 23 August 1926, son of Thomas Kieran Donegan, a former soldier in the Irish Guards who became a member of the Royal Corps of Commissionaires after the First World War, and his wife Anne, née Carley, a cook. He left school at sixteen and joined the United Dairies Engineering Company as a junior draughtsman from 1942 to 1945. After the Second World War he worked variously in advertising and technical drawing jobs. In 1953 he married Marie-Thérèse Le Bras, with whom he had a son and a daughter.
in 1958 he became art director of the advertising agency David Williams and Ketchum, until the early 1960s when he joined the staff of the Sunday Times, designing the Sunday Times Magazine when it was launched in 1962. He won the Designers' and Art Directors' Award for his poster designs in 1964. In 1968 he was appointed creative director of Sharps Advertising.
He started submitting cartoons to magazines in the late 1960s, and in 1975 he turned to cartooning full-time. He contributed cartoons and covers to Punch from 1975 to 1991, and drew a regular comic strip, Waldo, for the Sunday Express from 1981 to 1984. He directed a series of animated cartoons for television, including three Clixby shorts for deaf and speech-impaired children in 1983, and published a series of books of his dog cartoons, including Dog Almighty (1986), Dog Help Us! (1987), For Dog's Sake (1990) and the omnibus For the Love of Dog! (1990), and illustrated June Whitfield's Dog Tales: The Essential Companion for Dogs' Best Friends (1987), although he never actually owned a dog.
He retired with his wife to Brennilis in Brittany, France, in 1991, and died there on 27 April 2009.