The young Georgiana is contracted in marriage to William Cavendish, in order that he produce a male heir. A motherless child, Charlotte, comes to live with them. William expects Georgiana to mother the child. Georgiana gives birth to a girl. William is not pleased.
Georgiana socializes with Lady Bess Foster at Bath. She is invited to live with them since she has no where to go.
William has an affair with Bess. Georgiana feels robbed of her only friend. Bess explains to Georgiana that her motive is to regain contact with her three sons. Bess continues to live with them.
Georgiana starts an affair with Charles Grey. William is outraged that Georgiana should suggest that since he has Bess that she should have Charles. William rapes Georgiana; a male child is the result.
Bess encourages the affair between Georgiana and Charles. The Duke threatens to end Charles' political career and to forbid Georgiana from seeing her children again if she does not end the relationship. Georgiana ends her relationship with Grey, and she tells William that she is pregnant with Charles' child. She is sent to the countryside where she secretly gives birth to their daughter, Eliza Courtney. The child is given to the Grey family to raise.
Georgiana finds comfort in Bess' friendship, and gives permission for William and Bess to marry.
Georgiana in secret visits her daughter Eliza. Eliza named her own daughter Georgiana. Charles becomes Prime Minister.Keira Knightley as Georgiana Cavendish, Duchess of Devonshire
Ralph Fiennes as William Cavendish, 5th Duke of Devonshire
Hayley Atwell as Lady Elizabeth 'Bess' Foster
Charlotte Rampling as Georgiana Spencer, Countess Spencer, Georgiana's mother
Dominic Cooper as Charles Grey, 2nd Earl Grey
Aidan McArdle as The Right Honourable Richard Brinsley Sheridan
Simon McBurney as The Right Honourable Charles James Fox
Sebastian Applewhite as Sir Augustus Clifford, 1st Baronet
Calvin Dean as Devonshire House Servant
Emily Jewell as Nanny
Richard McCabe as Sir James Hare
Bruce Mackinnon as actor playing Sir Peter Teazle in The School for Scandal
Alistair Petrie as Heaton
Georgia King as actress playing Lady Teazle in The School for Scandal
Camilla Arfwedson as Lady Charlotte
The Duchess was produced by British Qwerty Films and American Magnolia Mae Films, with financial support from BBC Films, French Pathé and Italian BIM Distribuzione. The film was shot at Twickenham Film Studios and on location at Chatsworth, Bath, Holkham Hall, Clandon Park, Kedleston Hall, Somerset House, King's College London and the Old Royal Naval College in Greenwich.
Regarding lead actress Keira Knightley, director Saul Dibb said The Duchess was "a chance to take a character from late childhood – she's married at 17 – into full adulthood, 10 years later." It was also a chance for Knightley to work with Ralph Fiennes, whom she regarded as one of her most accomplished co-stars to date; Dibb said, "When I said, 'We've got Ralph interested in playing the Duke', we both took a gulp and went, 'F---.' [sic] ... But I didn't for one second feel that she wasn't up to the task." Originally the film was to be directed by Susanne Bier.
Studio executives wanted to use digitally altered images of Keira Knightley in promotional materials. The alterations were specifically aimed at enlarging her breasts. Knightley objected to the alterations, and they were not used. The marketing campaign also drew criticism for its use of Diana, Princess of Wales, who was an indirect descendant of Georgiana's. The advertising used slogans such as "two women related by ancestry and united by destiny" and used "There were three people in her marriage," the latter being an almost identical copy of a famous quote that Diana, Princess of Wales uttered during her Panorama interview. Michael Hellicar of the Daily Mail stated that "the Diana link is being so heavily, and it has to be said, so cynically and crudely promoted."
Amanda Foreman, author of Georgiana, Duchess of Devonshire, criticised the marketing strategy too, saying, "They probably thought the only way to get the young popcorn-eating brigade to see the film was if they thought it was about Diana, but it wasn't necessary and they should never have done that. And the line 'united by destiny' is wrong. I don't think Georgiana actually died in a carriage crash."
The BBFC has classified the film as a 12A, citing the scene of implied marital rape, which is "delivered through Georgiana's screams of protest, heard from outside the bedroom door." The BBFC's PG rating allows implied sex as long as it is discreet and infrequent; the board decided that the scene in The Duchess is more than "discreet" or "implied". The film had its world premiere on 3 September 2008, in Leicester Square and was released nationwide in the United Kingdom on 5 September.
The film received mostly positive reviews. Rotten Tomatoes gives a score of 61% based on 163 reviews, with the consensus that "While The Duchess treads the now-familiar terrain of the corset-ripper, the costumes look great and Keira Knightley's performance is stellar in this subtly feminist, period drama."
Most reviewers highly praised Knightley and Fiennes' performances. Time Out London wrote: "[Saul Dibb] is also helped enormously by a mature, restrained portrayal from Knightley, a masterclass in passive aggression from Fiennes and a performance of tender seduction from Atwell." The Epoch Times writes, "Ralph Fiennes brings a human quality to [the Duke] by avoiding any intent, exaggeration or ill will" and "Keira Knightley's performance gains new depth – she not only perfectly portrays a witty and feminine Georgiana early in the film, but also a caring mother, and an abandoned woman later on. Also remarkable in this role is Knightley's ability to portray the strengths, weaknesses, and the internal hurdles of Georgiana, as well as her internal contemplation." Film Ireland writes "It is a slow movie but it is well acted with Knightley and Fiennes suited to their roles, especially Fiennes who gives a formidable and powerful performance." Cameron Bailey, the co-chair of the Toronto International Film Festival comments, "The Duchess Of Devonshire, with Keira Knightley, which is a beautiful film and she gives a really mature performance. You're seeing her really turn into something beyond the kind of pretty face that we've seen her do already so well. But she's actually a very serious actress and she's turning into a great, great performer."
Peter Bradshaw of The Guardian wrote that "Dibb's movie looks good" but complained the film was "exasperatingly bland and slow-moving at all times" handing out a 2 of 5 star rating. However, Paul Hurley gave the film 8/10 and called The Duchess "an excellent new film" and states that "The Duchess stands a good chance of taking home some very big prizes at the end of the year".