The actress plays doomed young factory worker Fantine in Tom Hooper's adaptation of the beloved musical, in which each actor sang live during filming.
"The perspective is so spontaneous, and you're allowed to keep that and honour that and explore that, and be really moved by what's happening in the moment," Hathaway told Flicks and Bits. "In the film, I'm asking the audience to believe a lot of things.
"And there seems to me to be something selfish about trying to go for the pretty version of it, so I just sort of decided to apply the truth to the melody and see what would happen. I think it had a very freeing effect on us all."
She went on to admit that all her previous musical experiences on film have been pre-recorded, which made Les Misérables an entirely new challenge.
"It's not something I've ever been asked to do before, everything's always been pre-recorded," she explained. "I don't have extensive experience singing on film, but I loved getting to do everything spontaneously.
"Even to be able to turn the part of your brain off that you have to use when you're not singing in a film to match your performance. I loved that each take could live on its own, as its own unique expression."
The film received a standing ovation during a recent critics' screening in New York.
> Les Misérables: five new preview clips revealed - video
> Hugh Jackman, Russell Crowe, Anne Hathaway in 'Les Misérables' - pictures
Les Misérables will be released on December 25 in the US, and January 11 in the UK.
Watch a clip below: