The actress travelled to the African country to meet activist Amie Kandeh, who is a survivor of gender-based violence. Kandeh now works with the International Rescue Committee to support other victims of gender-based violence.
Mendes explained that she was not fully prepared for the effect her trip to the country would have on her, telling People: "I knew I was in for a life-changing experience.
"This experience has profoundly affected me. 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."
Mendes visited Sierra Leone as part of the PBS series Half the Sky: Turning Oppression into Opportunity for Women Worldwide, which is based on a best-selling book by Nicholas Kristof and Sheryl WuDunn.
Other stars featured on the series include America Ferrera, Diane Lane, Meg Ryan and Olivia Wilde, who were introduced to women in developing countries living in difficult circumstances ranging from sex trafficking and prostitution to maternal mortality.
Watch Eva Mendes talking about her involvement in Half the Sky below: