A young woman (Helen McCrory) tearfully leaves her son (Eugene Simon) to live with his grandmother and promises to return for him someday. Several years later, in 1753, in Venice, Casanova (Heath Ledger), is notorious for his promiscuity with women, his adventures being represented in puppet theatres around the city. The Doge, (Tim McInnerny) the ruler of the city, is a friend to Casanova, but cannot be too lenient on him as to avoid trouble with the church. He warns Casanova that he must soon marry or he will be exiled from the city. Casanova gets engaged to Victoria, famous for her virginity, to save himself from exile.
Casanova later meets and falls in love with Francesca Bruni (Sienna Miller), who writes illegal feminist books under the pseudonym of a man, Bernardo Guardi, and argues for women's rights as Dr. Giordano de Padua. Francesca mistakes Casanova's name for Lupo Salvato(casanova's servant) and Casanova goes with it as she hates ill-reputed Casanova. Her mother (Lena Olin) pressures her to marry rich Paprizzio (Oliver Platt), from Genoa, as settled by her late father, as they are heavily in debt. When Paprizzio arrives in Venice, Casanova lies to him and says that the hotel he booked is closed and he persuades him to stay at his house. Casanova also lies and says that he is indeed Bernardo Guardi. While Paprizzio asks his advice on how to impress Francesca, Casanova lures him to stay at home while receiving treatment for weight loss.Casanova visits Francesca, pretending to be Paprizzio and tells her that he lied to her before to make sure she is not in love with someone else and marrying him only for his money. Francesca initially distrusts him but starts gradually to trust him.
During the Venetian Carnival, Francesca recognizes the real Paprizzio from his publicity posters which force Casanova to confess his true identity making her angry. Casanova is arrested by the Venetian Inquisition for crimes against sexual morality, such as debauchery, heresy, and fornication with a novice. He saves Francesca by pretending to be Bernardo Guardi, which cools her anger. At his trial, Francesca confesses that she is the real Bernardo Guardi, and both are sentenced to death. Meanwhile, Francesca's mother and the real Paprizzio fall in love.
Just as Casanova and Francesca are about to be hanged in the Piazza San Marco, they are saved by an announcement that the Pope gave amnesty to all prisoners who were to be executed on that day, as it was the Pope's birthday. It is later discovered that the "Cardinal" who gave the announcement was actually an impostor who happens to be Casanova's stepfather, wedded to his long-lost mother who came back for him just as she promised when Casanova was a child.
As they all escape on Paprizzio's boat, Francesca's brother, Giovanni (Charlie Cox), stays behind to marry Victoria and to continue Casanova's legendary womanizing. The real Casanova spends the rest of his life as a stage actor touring with his family and the Paprizzios.
Filming began on July 9, 2004, and the finished film was released in the United States on September 3, 2005. Visual effects for the film were produced by Custom Film Effects and Illusion Arts. Period costumes were supplied by four different Italian costume houses: Tirelli Costumi, Nicolao Atelier, Costumi d'Arte, and G.P. 11, and shoes were manufactured by L.C.P. di Pompei. Wardrobe was also rented from Sastreria Cornejo of Spain.
Despite being set in Venice, some scenes were filmed in Vicenza, particularly the Teatro Olimpico, the Renaissance theater known for its intricate forced perspective stage design.
Concerto Grosso in D Minor, Op 3 No 11 (Vivaldi)
Concerto for Mandolin in C Major (Vivaldi)
Concerto No. 1 in C Major (Paisiello)
Concerto in B Flat (Durante)
Rotten Tomatoes gives the film a score of 44% based on reviews from 131 critics.