John Hayward was born in Yorketown, SA, the son of Dr Lionel Hayward. His grandfather, William Thornborough Hayward, was a notable South Australian and one of the first honorary physicians to the Adelaide Hospital. His mother was the daughter of Dr Alexander Lawrence. He was educated at St Peters College and the University of Adelaide, graduating with credit. He had a long association with the Royal Adelaide Hospital, first as RMO in 1933 to 1934 and subsequently as honorary clinical assistant physician from 1939 to 1947, honorary assistant physician from 1947 to 1956, honorary physician from 1956 to 1967 and finally, on retirement, honorary consulting physician. He was assistant physician, tuberculosis services from 1936 to 1947, working at the Adelaide Chest Clinic, and honorary visiting physician to the Kalyra Sanatorium from 1936 to 1952. He was also visiting physician, Repatriation General Hospital from 1963 to 1975, visiting physician, Home for Incurables from 1967 to 1975 and honorary consulting physician, Queen Victoria Maternity Hospital from 1945 to 1956. He gave up practice in 1976 after moving to Perth where his two surviving daughters were living.

The particular aspects of internal medicine which attracted him were respiratory medicine and psychosomatic disease. The physical manifestations of emotional disorders particularly fascinated him. Both interests were emphasized in his undergraduate teaching and his graphic demonstration of the hyperventilation syndrome was one to linger in the memory. He was a serious man, always courteous and correct. His manner was diffident and his speech hesitant. His handwriting was neat, flowing, minute and often baffling. His patients remember him with affection.

From 1941 to 1943 John Hayward served in the RAAMC and as a major saw active service as a physician in New Guinea from 1942 to 1943 with the 110 Australian CCS until overcome by illness, which led to his discharge. In 1935 he married Marie Moll in St Clement Danes Church in London. He had three daughters. He was a devoted family man and his main recreation was his home. Although a rower in his university days and captain of the Boat Club from 1930 to 1931, his subsequent sporting activities were confined mainly to social tennis. The early death of his eldest daughter suddenly in Switzerland was a great sadness in his later life.