Joyce Dennys was born in India to a military family during the British Raj. When her father retired, they went "home" to Devon in England. As a young woman, she enrolled at Exeter Art School and also studied art in London. During World War I, she served as a VAD (Volunteer Aid Detachment) nurse. In 1915, she was commissioned to illustrate the book Our Hospital ABC with verses by Hampden Gordon and M.C. Tindall, published the following year. She also produced recruitment posters for the British War Office. In 1919, she married Tom Evans, a physician, and moved with him to New South Wales, Australia. Her drawings were exhibited in many galleries there. In 1922, the family moved back to England, settling in Budleigh Salterton. She took part in the town's amateur theatricals as an actress and playwright and continued to produce illustrations for magazines such as Punch and Sketch. At the beginning of World War II, she created the character of "Henrietta" for an article for Sketch, which took the form of a humorous letter from Henrietta to a friend serving in the army. It was such a success that she was asked to continue to write letters as a regular feature in Sketch for several years. The articles were later collected in the book Henrietta's War (1985), and a followup volume was called Henrietta Sees It Through (1986).