Justin comes from a long line of pure-blood wizards. His parents lived in Lavelanet, France, before they moved to Sheffield, England in 2009. They are James and Lauren Whiteley. Both his parents went to Beauxbatons. He has one older brother who studied at Hogwarts, and was sorted into Gryffindor. He now works at the Ministry. Since his parents preferred to live a 'normal life', they were not particularly up-to-date with the magical world.

Justin is not a social person, and he does not like long, boring conversations. Since both his parents lived in France, he can speak French fluently. Although they were pure-blood, his parents did not dislike Muggles; a trait he shares.

Although his parents did use magic, it was not often, and his brother was not at home most of the time. Therefore, he did not notice magic much until his 6th birthday, when he and his best friend were cornered at school by a boy whom he had gotten into trouble with before. Eventually, he threw a punch at Theo, who was a relatively scrawny kid. He collapsed, clutching his face, with a steady stream of blood beginning to carve a path down his shirt. Justin flew into a rage. Suddenly, a light directly above them creaked and fell on top of them. No-one was seriously injured, and it was put down to a lucky accident for him. After a few weeks, the incident was forgotten by everyone except his family.