The 40-year-old actress played Cornelia in the previous instalment "Dawn of the Planet of the Apes".
Cornelia is the chimpanzee wife of apes leader Caesar, said The Hollywood Reporter.
Andy Serkis was previously confirmed to return as the chimp leader. Karin Konoval also returns as Maurice, the orangutan with a gentle soul, while Woody Harrelson will play a human villain known as the Colonel.
Filming for the movie began last week with Matt Reeves returning as director. The helmer marked the beginning of the production by sharing the first photo from the set.
"War for the Planet of the Apes" is the third film in the reboot franchise, which started with "Rise of the Planet of the Apes" in 2011.
The first movie in the original franchise was " Planet of the Apes" in 1968.