The 33-year old, known for other costume dramas including "The Duchess" and "Pride & Prejudice", portrays Sidonie-Gabrielle Colette during the early part of her life.
The story kicks off when she leaves her Burgundy village in late 19th century France to marry older writer Henry Gauthier-Villars, known as Willy.
Colette ghost-writes for him what becomes a successful and trend-setting novel, then pens several more under pressure from her husband. The film follows Colette as she has gay love affairs and eventually fights Willy for the books' rights.
"I feel unbelievably empowered by this story because it's a story of a woman who steps out from the shadow of a man and finds her own voice and lives her own truth and I found that incredibly inspiring," Knightley said at the premiere of the film at the BFI London Film Festival.
Knightley, who has a young daughter, made headlines this week after she penned an essay for the book "Feminists Don't Wear Pink (And Other Lies)" talking about childbirth. Some outlets accused her of criticising Prince William's wife Kate's polished looks coming out of hospital soon after labour.
"I think it's very interesting that certain parts of the media have ... misrepresented my meaning and exactly what I said," Knightley said.
"The comments that I made ... are completely about the culture that silences women's' truths and forces us all to hide and I absolutely didn't shame anybody in any way, in fact, quite the opposite."
The "Pirates of the Caribbean" actress was joined on the red carpet by her co-stars, including Dominic West, who described Colette and his character Willy as an "early exponent of the celebrity couples".
Director Wash Westmoreland said the movie was long in the making.
"This film has taken 17 years from writing it to getting on the big screen," he said. "It was originally from my co-writer, co-director and late husband Richard Glatzer, so to see his name on the big screen again really means a lot."
(With inputs from agencies.)