The British star - who is playing the role of student leader Marius in the Tom Hooper-directed project - is delighted he is in the film because it means his brother gets to see him in a new version of the stage show he likes.
He said: "When I was going through The Audition process, I'd get phone calls from my brother asking me, 'Have you heard?' Because when we were kids going on family trips we'd always sing it in the car. That particular musical, weirdly, is something my family love, so it is exciting."
He said: "I'm just starting to do vocal warm-ups for 'Les Miserables'. I am singing! I would be lying if I said I was completely cool with it. But I did sing a bit as a kid and my parents took me to see that play when I was younger - it's amazing what a following it has, and so many avid fans."