Custance was born in England. He received his early education there and came to Canada at age 19. He attended the University of Toronto where he obtained an M.A. in Hebrew and Greek. He also became a Christian during this time.

He went on to earn a Ph.D. in Biblical archaeology and anthropology. Between 1957 and 1972 he wrote the ten volume "Doorway Papers" that attempt to bridge the gap between a scientific and a Christian worldview.