Amanda Laura Bynes was born in Thousand Oaks, California, on April 3, 1986, the youngest of three children born to Lynn (née Organ), a dental assistant and office manager, and Rick Bynes, a dentist. Her father is Catholic and is of Irish, Lithuanian, and Polish descent. Her mother is Jewish, and was born to a Canadian couple whose families were from Poland, Russia, and Romania.

Later, Bynes attended a comedy camp at the Los Angeles Laugh Factory and was spotted by a Nickelodeon producer before being cast by the network. Bynes rose to prominence with her various roles in Nickelodeon’s All That for seasons three through six. She later became a regular member of Figure It Out (1997–1999). At the age of 13, she began starring in her own sketch comedy show, The Amanda Show (1999–2002). In 2002, Amanda began to establish her fan base with her debut film role in Big Fat Liar (2002) opposite Frankie Muniz, and a co-starring role in the WB sitcom What I Like About You (2002–06) with Jennie Garth, which gained positive reviews. She also made her voice-over debut in Charlotte’s Web 2: Wilbur’s Great Adventure and later in the 2005 animated film Robots.

She appeared on the cover of Vanity Fair’s July 2003 edition. Bynes was named one of Teen People’s “25 Hottest Stars Under 25” in 2006. In 2005 she starred the romantic comedy Love Wrecked.

In 2006, after What I Like About You ended, Bynes focused on her film career and starred the sport comedy film She’s the Man, based on William Shakespeare’s Twelfth Night. Bynes’ next role was Penny Pingleton in Hairspray. The film was a critical and commercial success. Hairspray went on to become Bynes’ most successful film at the time. Bynes was featured on the Hairspray soundtrack, which went on to get a Grammy nomination. Bynes was to reprise her role in Hairspray 2, but the sequel was canceled. In August 2007, Bynes teamed up with Steve & Barry’s to create her own fashion line called Dear, consisting of apparel and accessories. The line was cut short when Steve & Barry’s filed Chapter 11 bankruptcy in 2008. Bynes’ next role was in another comedy, Sydney White, released on September 21, 2007.

In 2007, Bynes described herself as Jewish, and also stated: “As far as religion, I was raised both. I learned about both Judaism and Catholicism. My parents said it was up to me to decide (which faith to adhere to) when I grew up. I’m sort of a spiritual person anyway. I haven’t decided yet on a religion. I don’t know yet exactly what I believe.”

In 2008, Bynes appeared in the Lifetime Television movie Living Proof as the student assistant of Harry Connick, Jr.’s character. In June 2009, she signed a two-picture deal with Screen Gems and co-starred the 2010 comedy Easy A, a critical and commercial success with many critics praising Bynes’ role. The other film would have been a starring role, but she decided to break the contract. Also in 2009 she was also originally set to star in the comedy Post Grad, but dropped out with no reason revealed and was replaced by Alexis Bledel, aggravating rumors that she was in personal trouble. In 2010, Bynes started shooting the comedy film Hall Pass but dropped out again and was replaced by Alexandra Daddario.

In 2008, Bynes briefly dated Seth MacFarlane after voicing a character in an episode of MacFarlane’s show Family Guy. In 2020, on her Instagram page, she announced her engagement to Paul Michael. Three weeks later, it was announced that they broke off the relationship, but this announcement was later revealed to be false. Michael stated that their Instagram accounts had been hacked. In March 2020, Bynes shared an ultrasound photo on her Instagram account, announcing that they were expecting their first child. She later deleted this post, and her lawyer confirmed that the couple were not expecting a child despite her initial claim.

In July 2010, Bynes announced an indefinite hiatus from acting, but stated in 2018 that she intended to return to television acting.

In 2012, Bynes was charged with driving under the influence (DUI) in West Hollywood. Two years later, the charge was dropped and she received a three-year probation. In May 2013, Bynes was charged with reckless endangerment and marijuana possession after she was found smoking in the lobby of her Manhattan apartment building. When officers entered her 36th-floor apartment, she allegedly threw a bong out the window. A New York County judge dismissed the case against her in June 2014.

In December 2013, Bynes enrolled at the Fashion Institute of Design & Merchandising in Irvine for 2014. In 2018, she received her Associate’s of Art degree in Merchandise Product Development and announced her intentions to start a bachelor’s degree program. In 2019, Bynes graduated from FIDM.

In July 2013, Ventura County sheriff’s deputies detained her after she allegedly started a small fire in the driveway of a stranger in Thousand Oaks. She was hospitalized under a 72-hour mental-health evaluation hold. Bynes’ parents filed for conservatorship of their daughter shortly after her hospitalization began. In August, Bynes’ mother was granted a temporary conservatorship over Bynes’ affairs.

In October 2014, Bynes accused her father of emotional and sexual abuse in a series of tweets; when her parents protested their innocence, Bynes tweeted that her father had never abused her, but “The microchip in my brain made me say those things but he’s the one that ordered them to microchip me”. Days later, Bynes’ mother again received conservatorship. Soon afterward, Bynes announced that she had been diagnosed with bipolar disorder. In August 2018, paperwork was filed to continue said conservatorship until August 2020.

In 2018, Bynes stated she had been sober for four years with the help of her parents. She also apologized for what she said on Twitter during her years of substance abuse: “I’m really ashamed and embarrassed with the things I said. I can’t turn back time but if I could, I would. And I’m so sorry to whoever I hurt and whoever I lied about because it truly eats away at me.”