Eloise Mumford, 27, will play Kate Kavanaugh, best friend and roommate of Anastasia Steele in the film adaptation of the bestselling erotic novel.
The actress has been seen in the TV series Lone Star and The River as well as the indie film Drones.
After the controversy surrounding the casting of Christian Grey, Dornan, 31, was asked how he felt about the role.
“There was a slight fear,” he said. “But beyond anything else, I was really f—ing excited.”