Daphne Reynolds (Amanda Bynes) lives a comfortable but unsatisfying life as a young American girl with a bright future. She has never met her father. She lives with her single mother, Libby (Kelly Preston) above a Chinese Restaurant in Chinatown, New York. Believing it is in his best interest, her mother left Daphne's father seventeen years ago because of his family's disapproval of their relationship; ultimately, his father's secretary threw her out of the house, without Libby having a chance to tell him that she was pregnant with their daughter.
Daphne flies to London to get to know her father, Lord Henry Dashwood (Colin Firth), who recently inherited an Earldom but has disclaimed his seat in the House of Lords to run for election to the House of Commons to eventually become Prime Minister with Alistair Payne (Jonathan Pryce) backing him up. At a hotel, she meets Ian Wallace (Oliver James), a local boy. She notices her father on the television during a news broadcast, and tells Ian that the politician is her father.
When Henry is informed of the existence of the daughter he never knew existed, he embraces the opportunity to connect with her at the urging of his mother Jocelyn (Eileen Atkins). Her appearance causes a controversy that endangers his political ambitions. Daphne tries to win the acceptance of her father's social circle but is repeatedly thwarted by his snobby, gold-digging fiancée, Glynnis Payne (Anna Chancellor) and equally snobby step-daughter-to-be, Clarissa Payne (Christina Cole).
Daphne has to ward off the advances of Armistead Stewart (Ben Scholfield), a sleazy upper-class boy whom Clarissa fancies. In the end, Daphne ends up throwing him into the Thames at the Henley Regatta when he tries to kiss her.
To please her father and his social circle, she abandons her old style and dons the upper-class sophisticated look. She is noted in the British newspapers because of this.
Due to her changing herself, Ian is disappointed and leaves when they were supposed to go to a concert which Daphne forgot about. During her coming-out party hosted by her father, she overhears Alastair talking to Glynnis about having "gotten rid of" Daphne's mother 17 years ago when he says how he thought he would have to do the same thing to Daphne. After Daphne tries to confront him about it, Glynnis grabs Daphne and locks her up. Glynnis then asks the band's lead singer, Ian, to announce the father-daughter dance. Glynnis, knowing that Daphne is locked up, uses this as a ploy to get Henry to dance with Clarissa. Libby rescues Daphne, but it is too late; Daphne witnesses Henry dancing with Clarissa. Daphne rejects her new self because it is not who she is. She returns to America, and restarts her work as a waitress. Henry announces in a ceremony he is no longer going to pursue his political career. On the steps on his way out, he discovers that Alastair knew about Libby's pregnancy. Henry punches Alastair in the face for concealing Daphne's existence. He then breaks off his engagement to Glynnis as it is implied that she also knew about Henry having a child.
Daphne is serving at a wedding, and the father-daughter dance begins. She thinks of Henry and what she left behind, and just then, Henry shows up by boat after a long flight from London. After asking him what he's doing there, Henry informs Daphne that, while on the plane, he wrote down something that he had to tell her at least two hundred times, but is unable to find the papers. He then says that he loves her for who she is and "wouldn't change one hair on her head". Daphne, overjoyed, accepts his love and instead of calling him Henry, refers to him as "Dad".
She finally gets the father-daughter dance she has been longing for her whole life, while Libby watches. Realizing that he still loves Libby, Henry informs Daphne that he has "a rather large present" for her. Ian shows up and cuts in. As he and Daphne dance, Henry goes to see Libby. He apologizes to her, Libby accepts his apology, and they kiss.
In the epilogue, Glynnis gets married to a wealthy nobleman and Clarissa marries Armistead Stuart (who still has a wandering eye). Alastair becomes a tour guide in London. Libby and Henry are married in a Bedouin ceremony. This time they make sure it is legal. Daphne gets into Oxford. As the credits start to role, Daphne, Ian, Henry, Libby, and Jocelyn have a family meal outside the Dashwood manor.Amanda Bynes as Daphne Reynolds Dashwood, the daughter of Henry Dashwood and Libby Reynolds.
Ella Desmond Oakley portrays Baby Daphne
Colin Firth as Henry Dashwood, the Earl of Wycombe and Daphne's long-lost father.
Kelly Preston as Libby Reynolds, Daphne's mother who works as a wedding singer.
Oliver James as Ian Wallace, Daphne's love interest in England.
Eileen Atkins as Jocelyn Dashwood, the Dowager Countess of Wycombe who is Henry's mother and Daphne's long-lost grandmother.
Jonathan Pryce as Alistair Payne, Henry's manager who is the father of Glynnis Payne and the grandfather of Clarissa Payne.
Anna Chancellor as Glynnis Payne, the gold-digging daughter of Alistair Payne, the mother of Clarissa Payne, and the fiancée of Henry.
Christina Cole as Clarissa Payne, the daughter of Glynnis Payne and the granddaughter of Alistair Payne.
Sylvia Syms as Princess Charlotte
James Green as Percy, Henry and Jocelyn's butler.
Tara Summers as Noelle
Ben Scholfield as Armistead Stuart, a sleezy upperclass boy with a wandering eye.
Roger Ashton-Griffiths as Lord Orwood, the father of Peach and Pear Orwood who often talks about how he acquired his chandelier which often annoys Henry.
Cassie Powney as The Hon. Peach Orwood, the twin sister of Pear Orwood.
Connie Powney as The Hon. Pear Orwood, the twin sister of Peach Orwood.
Peter Reeves as Sir John Dashwood
Peter Hugo as Prince Charles
Matthew Turpin as Prince William
Chris castle as Prince Harry
Stephanie Lane as Fiona
Nita Mistry as Girl in Hostel
Elizabeth Richard as the Elizabeth II
What a Girl Wants received mixed reviews from critics. On Rotten Tomatoes, the film has an approval rating of 35% based on 104 reviews, with an average rating of 5.4/10. The site's critical consensus reads, "Little girls will definitely enjoy it, but it's too syrupy and predictable for adults." On Metacritic, the film has a score of 41 out of 100, based on 27 critics, indicating "mixed or average reviews".
The San Francisco Chronicle called it a "dreadful teen comedy." The Village Voice described the film as "a sanitized adventure for the Mary Kate-and-Ashley set."
In its opening weekend, the film grossed $11.4 million in 2,964 theaters in the [United States and Canada, ranking #2 at the box office behind fellow newcomer Phone Booth ($15 million). By the end of its run, the film grossed $36.1 million domestically and $14.6 million internationally, totaling $50.7 million worldwide.
Before the US release of the film, print advertisements were altered to remove the peace sign that Bynes was giving in the poster. A rep for Warner Bros. explained "'In a time of war, we made a slight alteration so that we could avoid any potential political statement in a completely nonpolitical film."