Based on the best-selling book by Nicholas Kristof and Sheryl WuDunn, the new series Half the Sky: Turning Oppression into Opportunity for Women Worldwide introduces Mendes and other stars, including America Ferrera, Diane Lane, Meg Ryan, Gabrielle Union and Olivia Wilde to women and girls living under difficult circumstances, ranging from maternal death to prostitution.
Mendes, 38, kicks off the four-hour series – airing Oct. 1 and 2 at 9 p.m. ET on PBS – with her visit to Sierra Leone, where she meets with activist Amie Kandeh, a survivor of gender-based violence working with the International Rescue Committee to help other survivors toward safe, productive futures.
"I knew I was in for a life-changing experience," Mendes says of participating in the project.
"This experience has profoundly affected me," she says. "I was so shocked and saddened to learn the extent of gender-based violence taking place in Sierra Leone every day and that trip has made me want to be a part of the solution."
See Mendes meet and exchange necklaces with Fulumatu, a young girl who bravely pressed charges against her rapist in the clip below.