Samantha Barks says she had to audition over 15 weeks for the part of Eponine in Les Miserables.
She previously competed in the BBC One musical programme I'd Do Anything, eventually finishing third in the reality television show.
Les Miserables is nominated for nine awards at this year's Baftas.
The actress was speaking to Newsbeat's entertainment reporter Natalie Jamieson.
Les Miserables is released in the UK on 11 January.