Heward was born in Montreal, Quebec, Canada, on July 2, 1896, into a well-to-do family. Prudence Heward was the sixth of eight children, including Dorothy, Barbara, Jim, Chilion, Honor, Rooney Heward. Prudence Heward was born to Sarah Efa Jones and Arthur R.G. Heward. Her father worked for the Canadian Pacific Railway. The family lived in a huge house in Montreal, spending summers at Fernbank, near Brockville, Ontario.