Emma D'Arcy was born on June 27, 1992 in London. According to The Cinemaholic, their parents are Sally Elizabeth and Richard John D'Arcy and their sibling is the non-binary dancer Chloe "Loe" D'Arcy.

While D'Arcy hasn't spoken much about their childhood, they did reveal that it wasn't exactly conventional. In fact, in an interview with Hey U Guys, D'Arcy explained that their family had "strong relationships with the spiritualist church." "It's great, it's like going — sort of similar to going to a Church of England service, except that sort of in the middle when you might have someone talking for ages, there's a medium who communes with people who've passed for 40 minutes," they explained. "And arguably of the two, I'd say that's more interesting and entertaining."

While D'Arcy isn't an active member of the spiritualist church, their upbringing taught them to be open to all kinds of spiritualism. "I'm open, and my dear, dear grandma passed a couple of years ago, and she was fully immersed in this spiritualist church, and so I will always stay open in case she wants to pay a visit."

In addition to spiritualism, D'Arcy was also exposed to the world of sci-fi as a kid. "Growing up sci-fi was sort of my area, my dad is a huge sci-fi addict," she told one interviewer. "In a big way, that was my entry point to storytelling."