She rose to prominence in 2004 with the success of her number-one debut album Autobiography.

Her reality series, The Ashlee Simpson Show, aired for two seasons. Following a North American concert tour and a film appearance, Simpson released her second number-one album, I Am Me (2005). Simpson assumed creative control over her third album, Bittersweet World (2008).

Simpson was born in Waco, Texas and raised in the Richardson area of Texas. She is the daughter of Tina Ann (ne Drew), a homemaker, and Joe Truett Simpson, a former psychologist and Baptist youth minister who works as Simpson's agent.

Simpson's older sister is Jessica simpson, who is also a singer and actress. She attended the same schools as her sister, Prairie Creek Elementary and Richardson North Junior High.

When Simpson was three years old, she began studying classical ballet. Simpson enrolled at the School of American Ballet in New York City in 1995, a year in advance.Her parents made the decision to relocate to Los Angeles, California for Jessica's singing career in 1999. Subsequently, Ashlee was cast in television commercials.

Eventually, Simpson made appearances in films and television series, including Malcolm in the Middle (2001), a minor role in The Hot Chick (2002), and a recurring role on the family drama series 7th Heaven (2002, 2003, and 2004).

In the summer of 2003, she worked as a video personality for MTV. Occasionally, Simpson appeared on Newlyweds: Nick and Jessica, a reality show documenting the married life of her sister Jessica and her then-husband, Nick Lachey.

Following the success of her sister Jessica's first album, Ashlee became one of her backup dancers. Simpson recorded a song entitled "Christmas Past, Present and Future" in 2002 for the holiday album School's Out! Christmas, which was later re-released on Radio Disney Jingle Jams in 2004 and 2005.

In the summer of 2003, she released a song called "Just Let Me Cry" for the soundtrack to the film Freaky Friday. After that Simpson signed a record deal with Geffen Records.

Her first album, Autobiography, debuted at number one in the United States in July 2004, with first-week sales of around 398,000 copies. The album was certified triple-platinum by the RIAA in September 2004. Simpson co-wrote all of the album's tracks, describing it as "very true to my emotions", however, critical reviews were mixed.

At the Teen Choice Awards on August 8, 2004, Simpson received the "Song of the Summer" Teen Choice Award for "Pieces of Me", as well as the "Fresh Face" Award.She also won the Billboard Award for New Female Artist of the Year in December, and in the same month, Entertainment Weekly named her one of its Breakout Stars of 2004.

As an accompaniment to her debut album, Autobiography, and to create interest in the beginning of her own music career, she filmed and appeared on her own reality television series, The Ashlee Simpson Show, which aired in the time slot following Newlyweds. It ran in the United States for 8 weekly episodes over the summer of 2004 . The show dealt with the processes of writing, recording and performing Simpson's music, as well as aspects of her personal life.

Simpson's second album, I Am Me, was released on October 18, 2005. She wanted to incorporate the feel of music from the 1980s on the album, and unlike with her debut, she wanted to focus less on relationships and more on herself.The album debuted at number-one.

Simpson began a concert tour in late September in Portland, Oregon and appeared on the October 8, 2005 episode of SNL to promote the album. The first song she performed on the show was "Catch Me When I Fall", a ballad written about her previous SNL experience

In March 2006, Simpson won an MTV celebrity surfing invitational competition, which also featured celebrities such as Meagan Good, Jack Osbourne, Ashley Parker Angel and Tony Hawk. On April 12, 2006, she hosted and performed at the MTV Australia Video Music Awards, where she won "Best Female Artist" and "Best Pop Video" for the single "Boyfriend".

During 2007, Simpson recorded her third studio album, Bittersweet World, She described the album as being influenced by 1980s music—bearing similarities with I Am Me—while still incorporating elements of rock and pop and described her intention to go on tour to support the album. Bittersweet World was released in the United States on April 22, 2008 to mixed reviews.

Simpson returned full-time to television episodes by playing the role of Violet Foster in Melrose Place, the CW's revamp of the '90s series of the same name. post that she reprised her role in the Broadway musical production of Chicago. She began her Broadway run on November 30, 2009 and performed in New York for eight shows a week until February 7, 2010.

In April 2008, Simpson and Wentz confirmed their engagement and were married . 2weeks later, Simpson confirmed her pregnancy. On February 9, 2011, Simpson filed for divorce from Wentz, citing irreconcilable differences. Their divorce was finalized on November 22, 2011.

Simpson launched a collection of tops in partnership with the clothing retailer Wet Seal on April 22, 2008, the same day Bittersweet World was released. She also began appearing in commercials for Canadian retailer Zellers to promote their independent clothing line, Request, in mid-2008. Simpson appeared on the second episode of The CW's America's Next Top Model, Cycle 17 as a guest judge. She created a fashion line aimed at girls aged 7–16 in collaboration with her sister's successful brand. Simpson is the co-creative director of the line, which was released in the winter of 2011.

When Simpson first broke onto the music scene in 2004, she was set apart from her sister's already established image due to a different music style, different fashion choices, and a more assertive personality.

Simpson's songs have been characterized by rock elements absent from her sister's music, and, particularly during her early career, Simpson would often wear outfits highlighting a rock or punk-influenced sense of style.

She cites her childhood as being the time when she began to sing, and admits that she dreamed of being on Broadway and did not expect to break into the pop music scene.She trains with a vocal coach, and studies Etta James and Aretha Franklin albums for vocal inspiration

She has cited Gwen Stefani, No Doubt, Joan Jett, The Runaways, Madonna, Pat Benatar, Green Day, Alanis Morissette, Fiona Apple, Chrissie Hynde, and Debbie Harry from Blondie as her musical influences.