His name had been bandied about recently for the newest Mad Max, although Australian paper The Daily Telegraph was putting Sam Worthington in the role earlier this week.
Theron next appears in The Road.
The logline on the script is being kept under wraps, but the Heat Vision blog says the movie takes place a short while after the story detailed in the last Max movie, Thunderdome.
Doug Mitchell is producing with Miller. Warner Bros. is set to distribute.
Miller had announced last weekend that preproduction work was starting in New South Wales, but he didn't give any indication as to whether Mel Gibson might return or who would play the male lead. "It could be Mel, it could be anyone," he told reporters.
Miller and the 21-year-old Gibson launched their careers with Mad Max in 1979. Sequels came in 1981 with The Road Warrior and in 1985 with Mad Max: Beyond Thunderdome.