The Hollywood stars are both committed to living a meat-free lifestyle.
E! Online reports that non-profit animal rights organisation People for the Ethical Treatment of Animals (PETA) is elated to honour Chastain and Harrelson for their choice to be meatless.
Chastain stopped eating animals 15 years ago.
She spoke previously about how she managed to gain nearly 15lbs for her Oscar-nominated role in 2011's The Help on a strict vegan diet.