The little known star shot to fame on U.K. TV talent show I'd Do Anything, competing to land the part of Nancy in Mackintosh's Oliver! musical.
She was performing in the show at the Palace Theatre in Manchester, England on Tuesday (31Jan12) when Mackintosh walked onto the stage during the curtain call to inform her she had won the coveted part of Eponine in director Tom Hooper's big screen adaptation of Les Miserables.
He told the audience, "For the last few months in Broadway, Hollywood and London we have been searching (for Eponine) - now I can reveal director Tom Hooper has chosen her (Barks) for the movie."
Barks, who played Eponine in Mackintosh's West End version of the show, is said to have seen off fierce competition from stars including Scarlett Johansson, Lea Michele and Taylor Swift to land the role, and she admits she was stunned when the producer delivered the news.
She tells BBC Breakfast, "I had absolutely no idea (that was going to happen)... I was there taking my bow and the next moment Cameron Mackintosh walks on to the stage with that news. It surprised me. I am still shocked. It's an incredible cast. I'm very excited to meet them and work with them all... I just played her in the West End for the year and now it's the movie..."
Barks will star alongside Hugh Jackman, Anne Hathaway, Russell Crowe and Amanda Seyfried, and production is scheduled to begin in March (12).