The married Dickens had a longtime affair with a much younger woman. Fiennes, who also directs the movie, realized to tell the story truthfully, he'd have to show Dickens, warts and all.
"If you tell the story of Nelly Turnan and Dickens, you're going to have to tell the story of the way Dickens left his wife and the cruelty of that," said Fiennes. "I feel a bit protective of Dickens because I kind of like him, but I see there is this unhappy, unattractive moment in his life. But if you...you have to be careful not to forget all the other things that he did."
Doing double duty as director and actor proved to be a challenge for the Oscar winner.
"It was kind of mad to want to do both, but you can do it, you just need to have a lot of time and a great support system," he said. "The days when I was not playing Dickens were great. It always was a bit of a head squeeze, like my head in a vice when I was doing both on one day. On days when I didn't have to be Dickens, and there were few of them, it was always, 'Ah, now I can just focus on directing and the other actor and the camera, whatever.'"
Fiennes has been acting for 25 years, and whether he's playing a quieter role like Charles Dickens, or filling the screen with the big budget glory of Harry Potter's nemesis Lord Voldemort, he's happy as long as he has a character to explore.
"To have a chance to play across a spectrum of kinds of roles or kinds of movies or theatre for that matter, it's great, it's great to have different arenas," he said.
"The Invisible Woman" is rated R and is in theaters now.