Darvill is best known for portraying Rory Williams on the BBC series "Doctor Who." He has also appeared on stage in Our Boys, Dr. Faustus, Swimming with Sharks, Marine Parade, Stacy and Terre Haute. He will take on the role of Guy.
Christie, who steps into the role of Girl, co-starred with Daniel Radcliffe in the West End revival of Equus. She has appeared in "Mr. Selfridge" as well as The Ramshackle Heart and One Night In November.
Once is directed by John Tiffany (Black Watch), with movement by Steven Hoggett (Black Watch, American Idiot) and music supervision and orchestrations by Martin Lowe (Mamma Mia!). It won eight Tony Awards including Best Musical.
The production has set and costume design by Tony Award winner Bob Crowley (The Coast of Utopia, Mary Poppins). Lighting design is by Tony winner Natasha Katz (Aida, The Coast of Utopia), and sound design is by Clive Goodwin.
Visit oncemusical.com for more information.