"The gorgeous and talented Charlie Hunnam will be Christian Grey in the film adaptation of Fifty Shades of Grey," she wrote.
Hunnam currently stars as a series regular on the hit FX biker drama, which returns for its sixth season on Sept. 10. His film credits include Pacific Rim, Children of Men, Cold Mountain, Nicholas Nickelby and Green Street Hooligans.
Fifty Shades of Grey will be released by Focus Features on Aug. 1, 2014, in North America.
The announcement rounds out the major casting for the highly anticipated project, which is being directed by Sam Taylor-Johnson and produced by Michael De Luca and Dana Brunetti alongside author James. Kelly Marcel wrote the screenplay.
Fifty Shades follows college student Anastasia Steele (Johnson) as she begins a racy relationship with the 27-year-old billionaire, Grey.