The sexy star admits she once wore fur to a Hollywood event, but she'll never repeat her mistake.
And, by way of repenting, she's hosting a new Internet expose about the fur industry.
The film includes the latest investigation of fur farms and markets in China, the world's largest fur exporter.
Mendes tells WENN, "Millions of animals are killed for their pelts each year... I didn't always know how animals were killed for their fur, and I even wore fur once myself.
"When I learned how cruel the fur industry is - and that there are no laws protecting these animals - I swore that I'd never wear it again. Please join me today as we go behind the scenes of the international fur trade, and find out how you can look glamorous without supporting animal suffering."
Mendes admits she has become a leading celebrity animal rights advocate after her pet dog Hugo came into her life.
She explains, "It literally changed my life, getting my dog. Every choice that I make, I always think about my little Hugo and think, 'God, would I eat him? Would I cage him up? Would I skin him?' No, of course not."
Mendes joins a growing list of celebrities fronting various PETA anti-fur campaigns - they include Charlize Theron, Christina Applegate, Roselyn Sanchez, Pamela Anderson, Nia Long, and Christy Turlington.