Rebecca Ferguson's voice was dubbed by Loren Allred. Ferguson had studied music and admitted that she can carry a tune but since Jenny Lind, her character, is considered the best singer in the world, dubbing her voice would be in service of the movie. However, in order to get into the role, Ferguson insisted on singing the song in front of the extras while filming.
According to Hugh Jackman, the film's nine-year development process from conception to completion was, in part, due to studios' unwillingness to take a risk on an original musical. What finally sold the deal at 20th Century Fox was the future Oscar-nominated song "This is Me," which Benj Pasek and Justin Paul wrote during the two-hour flight to the studio meeting where the film was greenlit.
Anne Wheeler played by Zendaya is most likely based on Anna Olga Albertina Brown, alias Miss La La. Edgar Degas painted her as the subject of "Miss La La at the Cirque Fernando" in 1879. She was an Afro-German trapeze star. Miss La La married an African American contortionist named Emmanuel Woodson, and they had three daughters.