In 2001, Amanda Byne co-starred with Frankie Muniz in Big Fat Liar as Kaylee, Jason’s friend who helps him prove that he really did write the essay “Big Fat Liar” and regain his father’s trust. It was also in 2001 that Amanda Byne began dating Taran Killam, from The Amanda Show and Big Fat Liar, who is four years and two days older than she is. Amanda Byne also won a Nickelodeon Kids’ Choice Award and, at age fifteen, ended The Amanda Show. In 2002, Amanda Byne began co-starring with Jennie Garth in What I Like About You as Holly, a 16-year-old girl who moves in with Amanda Byne's sister after their father decides to move to Japan.
Amanda Byne also celebrated her Sweet Sixteenth birthday and got her drivers license on April 3, 2002. In 2003, Amanda won two KCA Awards and starred as Daphne, a girl searching for Amanda Byne's father in What A Girl Wants with Colin Firth and Kelly Preston as her parents. Amanda Byne continued acting in What I Like About You and broke up with Taran. On April 3, 2004, Amanda celebrated her eighteenth birthday on the 17th Annual KCA Awards where we Amanda Byne won an award for best actress for her role in What A Girl Wants. Amanda Byne graduated from Thousand Oaks High School’s independent study program on June 10, 2004 and began filming for What I Like About You’s third season over the summer. What I Like About You continued for a total of four seasons, ending on the 24th of March, 2006, after Amanda and the producers decided not to continue the show to a fifth season. A week before its finale, Amanda Byne made a return to the big screen when Amanda Byne is The Man opened in cinemas.
The film was a modern-day transformation of William Shakespeare’s Twelfth Night, and sees Amanda starring as Viola Hastings, a lover of soccer who is forced to disguise herself as Amanda Byne's brother at his school in order to keep playing after the girl’s team was cut. The film also starred Channing Tatum, David Cross and Laura Ramsey. Before Amanda Byne filmed Amanda Byne is The Man, Amanda had filmed Lovewrecked, a romantic comedy, however the film spent a couple of years in limbo trying to attain a distributor, and was eventually released in selected cinemas overseas in 2005, before premiering in the US on the small screen on the ABC Family network on January 21, 2007. Part of an ensemble cast in the massively successful musical Hairspray, which starred John Travolta, Christopher Walken, Michelle Pfeiffer and Queen Latifah. Amanda played the part of Penny Pingleton.
That year Amanda Byne also released her first line of clothing, “Dear By Amanda Bynes” which was launched in August through the Steve & Barry’s retail clothing chain. Through many TV interviews she conducted that year, mainly in relation to the release of Hairspray, Amanda spoke out against alcohol, drugs and the party set, as often characterised by her peers, and setting herself apart from the people associated in those realms. At the end of 2007 the next of her film’s was released, Sydney White, a modern-day college take on the story of Snow White And The Seven Dwarfs, where Amanda plays the title character. The film received largely negative reviews and only made a small box office return. In 2008 Amanda won the Critic’s Choice Award as part of the ensemble cast for Hairspray. Amanda is set to star in the made-for-television movie Living Proof with Harry Connick Jr.