John Winthrop Hackett was born on November 5, 1910 in Perth, Australia. His father, also Sir John Winthrop Hackett, who was of Irish descent, owned two newspapers. His mother was Deborah Drake-Brockman. Her parents were prominent members of Western Australian society - Grace Bussell, famous for rescuing shipwreck survivors as a teenager and Frederick Slade Drake-Brockman, a prominent surveyor and explorer. John Winthrop Hackett had four sisters: Verna Hackett, Joan Hackett, Patricia Hackett, and Deborah Winthrop Hackett.