Kirby is a trained ballerina and studied at the Royal Ballet School in London before pursuing acting.
Kirby once worked as a receptionist at a dental practice to make ends meet while auditioning for acting roles.
Kirby has a tattoo of a bird on her right wrist, which she got in honor of her grandmother.
Kirby is a big fan of the English football team Arsenal and has attended several matches.
Kirby is a vegetarian and has been known to speak out on animal rights issues.
Kirby is a close friend of fellow British actress and "The Crown" co-star Claire Foy.
Kirby has been open about her struggles with anxiety and has spoken out about the importance of mental health awareness.
Kirby is a big fan of the "Harry Potter" book series and has said that she would love to be in a "Harry Potter" movie.
Kirby is trained in stage combat and has performed in several productions that required her to do fight scenes.
Kirby has a passion for travel and has visited countries all over the world, including Japan, Brazil, and Iceland.