Fantine's assault by a rejected customer is based on an actual incident from Victor Hugo's life that resulted in Fantine's creation: he was on his way to his editor's office when he encountered a young man harassing a prostitute. When she rejected his advances, he shoved a handful of snow down her dress and shoved her to the ground. When she defended herself with her fists, he immediately called the police to arrest his "assailant". Hugo was a minor celebrity at the time, and spoke up on the woman's behalf when the police arrived, and was able to have her set free. Hugo said he was horrified by the unfairness of the woman's situation, and began to imagine that she might have children depending on her, and thus Fantine appeared in his mind.
Hugh Jackman lost considerable weight and went 36 hours without water, causing him to lose water weight around his eyes and cheeks, giving him the gaunt appearance of a prisoner. He also grew a real scraggly beard for scenes of Valjean as a prisoner, though mercifully they were shot first in production and he could shave and return to his usual weight for scenes playing Valjean as a wealthy man.
The soundtrack for a movie musical is usually recorded several months in advance and the actors mime to playback during filming. On this film however, nearly every song was recorded live on set to capture the spontaneity of the performances. Everyone involved, from Hugh Jackman to Russell Crowe to producer Cameron Mackintosh, praised this approach as it allowed them to focus more on their acting and performances. They also praised director Tom Hooper for attempting this on such a scale; something no director has ever done before. The opening song Look Down, set in the dock yard, did have to be prerecorded due to the loud water and other ambient noises in the scene.
Colm Wilkinson, who plays the Bishop, is the original Jean Valjean from the original English language Les Misérables stage productions, in both London in 1985 and on Broadway in 1987. He has also reprised the part in several of the concert versions, most notably in Les Misérables in Concert (1995) as part of "The Dream Cast" for the musical's 10th anniversary.
Anne Hathaway actually allowed her hair to be cut very short for the scene where Fantine's hair is cut. Her male hairdresser was put in a dress to double as the haircutting woman, actually cutting Hathaway's hair on set.