EW.com reported the casting news Thursday.
The Hollywood Reporter said Cavill -- who is known for playing Superman in Man of Steel, Batman v Superman: Dawn of Justice and Justice League -- will play the older brother of aspiring detective Enola, who is being portrayed by Stranger Things standout Millie Bobby Brown.
The project was announced in January 2018.
The Legendary Entertainment film is based on Nancy Springer's Enola Holmes Mysteries novel series.
Helena Bonham Carter is playing Enola's mother in the screen version.