John "Jack" Greenall was born on 12 January 1905 in Whitefield, Lancashire. His first strip was "Pa, Ma and the Boy" in Pictorial Weekly from 1929, and he also contributed to magazines like Punch, Bystander, Passing Show, Ideas and Razzle, and comics including Sparkler and Jolly Comic.
He drew the single panel cartoon "Useless Eustace" for the Daily Mirror from 1935. Eustace was started out as a hapless office worker, but as the series went on he performed whatever occupation suited the cartoon's humour. He also featured on postcards, and a female counterpart, "Useless Eunice", appeared in the Woman's Sunday Mirror supplement. After Greenall's retirement in 1975 the cartoon, then simply "Eustace", was drawn by Peter Maddocks.
Greenall also drew "Billy and Brenda Brown of London Town" for the magazine Everyday Novels and Comics in 1940. He died in Lancing, Sussex, in July 1983.