"I saw the musical when I was 11 so I became obsessed immediately," she said.
Seyfried fell in love with "Les Miserables," the popular musical set in 19th century France.
"I was meant to do this," she said. "I mean, it's funny, when I was talking about 'Mama Mia,' people kept asking, 'What's your favorite musical?' 'Well, it's "Les Mis," but god knows when they're going to make that movie.' And luckily, they made it now because I'm of age to play these characters and it, you know, I feel it's in my soul somewhere."
Maybe because as a kid, she had already tackled the material.
"I did it for a night in a recital. I sang 'Heart Full of Love.' That was like the beginning of learning, of studying classical music," she said. "Like I went into opera at that point, and then I quit when I was 17."
Everyone in the cast sang live, performing their songs in the movie. Seyfried says it was akin to them all jumping out of a plane together.
"You've got these amazing movie stars, talented actors, and then you've got me, you know, who's semi-experienced and then you've got Samantha who's never done a movie before. And everybody has their own insecurity," she said. "And together, as a team, we had this collective excitement/anxiety about it."
Seyfried has several projects on the way. Among them: her turn as the late adult film star Linda Lovelace in "Lovelace."