The “Let Go For Tonight” singer, 25, will join new Time Lord Peter Capaldi and side kick Jenna Coleman for an episode in August.
“I can’t believe I’m actually going to be in an episode of Doctor Who!” she said, adding that her casting was a result of a chance meeting.
“I was playing a gig and got chatting to the show’s production team who’d been watching my performance,” Foxes continued. “I was telling them how much I loved Doctor Who and next thing they invited me to be on it.
“I couldn’t think of a better place to make my acting debut than on one of the UK’s most iconic shows!”
Steven Moffat, executive producer, said: “We are completely thrilled that the amazingly talented Foxes is joining us on board.”
The showrunner refused to let plot details slip but dropped a hint that “the Doctor is finally catching up on his phone calls”.
Foxes, real name Louisa Rose Allen, already has three hit singles and a Grammy under her belt. Her debut album, Glorious, recently entered in the top five of the Official UK Albums Chart.