He is the son of Mungo Ballardie MacCallum (1913-99), a journalist and pioneer of television in Australia, and Diana Wentworth, a great-granddaughter of the Australian explorer and politician William Charles Wentworth (1790-1872).
MacCallum was born in Sydney and educated at the elite Cranbrook School, a short walk from where he lived with his mother and father in his grandmother's house in Wentworth Street, Point Piper.