The film will be directed by Justin Kurzel and is based on a novel of the same by Peter Carey, according to The Hollywood Reporter.
The story is about notorious bushranger Ned Kelly (Mackay), one of the world's greatest outlaws.
Shaun Grant will write the screenplay for the film, which also features Essie Davis, Travis Fimmel and Dacre Montgomery.
The project is being produced by Liz Watts, Hal Vogel, and Brad Feinstein with Peter Carey, David Aukin, Vincent Sheehan, and Joseph F Ingrassia serving as the executive producers.