In the new drama, The Theory of Everything actor plays Einar Wegener, one of the world's first-known recipients of gender reassignment surgery who became a woman named Lili Elbe.
The casting has been criticised by several activists who claim the role should have been played by a member of the transgender community, but director Hooper is adamant Redmayne was the right choice.
He tells Screendaily.com, "Eddie was really the person I wanted to make the film with, and I was very passionate about that. I was a great believer in him as an actor. I think also there's a certain gender fluidity that I sensed in him, that I found intriguing... I felt that there was something in him that was drawn to the feminine...
"I think there's a tremendous pool of talented trans actors out there, and I think there's probably a journey to go on to make sure that talented trans actors have the same access to opportunities both in front of and behind the character as cisgendered actors.
"I hope we're at the beginning of a revolution that will improve access for trans actors and trans filmmakers - but there's a long way to go."
The Danish Girl is due for release in the U.S. in November (15) and in the U.K. in January (15).