Redford praised the heir to the British throne, speaking Thursday at the launch of the first-ever Sundance film and music festival.
He says Charles "has been committed for a long time, which I greatly admire, to sustainability and environmental conservation" and said working together "seemed like a natural fit."
Sundance London will host the royal premiere on Saturday of "Harmony: A New Way of Looking at Our World." The documentary by filmmakers Stuart Sender and Julie Bergman Sender maps out three decades of environmental work by the prince.
The Sundance London festival runs from April 26-29 at London's O2 Arena.