Simpson released her first single, "I Wanna Love You Forever," which peaked at #3 on the Billboard Hot 100 in 2000. Soon afterward her major label debut album Sweet Kisses was released. To support the album, Simpson toured with Ricky Martin and boy band 98 Degrees. Simpson and 98 Degrees group member Nick Lachey began dating shortly afterwards. After dating for two years, the couple cooled their relationship. After the September 11, 2001 attacks, the couple reconciled. Simpson stated, "After 9/11, I knew that I never ever wanted to be away from Nick ever for the rest of my life."
Meanwhile, Simpson's album Sweet Kisses had gone double platinum, helped by follow-up singles "Where You Are" and "I Think I'm In Love With You", which were both released in 2000. The latter became Simpson's biggest radio hit at that point, and was her first release of an uptempo single. Although her debut album sold 2 million copies, sales fell far short of those achieved by Britney Spears and Christina Aguilera, and unlike the two pop princesses, Simpson was not a worldwide household name. Columbia Records officials reportedly decided Simpson needed a change for her second album.
In 2001, Simpson recorded a follow-up album with what Columbia considered more radio-friendly, up-tempo tracks. The result in that was Irresistible, released in mid-2001 on the heels of the title-track first single. "Irresistible" became one of the biggest hits of her career; it peaked at # 15 on the Hot 100. Irresistible debuted at #6 in June 2001 on the Billboard 200 Album Chart, and has sold 825,000 copies to date.
In 2006, Simpson then returned to the recording studio, switching labels from Columbia to Epic Records. Her fourth album, A Public Affair, was released on August 29, 2006 via Epic Records. The album debuted at #5 on the Billboard 200 with 101,000 copies sold in its first week. The first single, "A Public Affair" (#14, 2006), reached the Top 20 of the Hot 100 but quickly fell off the charts. The music video for "A Public Affair" featured Eva Longoria, Christina Applegate, Christina Milian, Maria Menounos, Andy Dick and Ryan Seacrest. A second single, "I Belong To Me," was also released through her website and is now included on the CD itself. The single's video appeared on TRL countdowns, but quickly fell off.
In December 2006, while performing a tribute to Dolly Parton at the Kennedy Center Awards, she botched the lyrics, getting flustered in front of a crowd that included prominent persons such as Steven Spielberg, Shania Twain, and President George W. Bush. Though Simpson was given the chance to redo the song for cameras, her portion was edited out of the CBS broadcast.
In September 2007, Simpson's father Joe Simpson stated to People magazine on September 11, 2007, that Simpson was considering doing a country album. Joe Simpson told People that she is "talking about doing a country record and going back to her roots, being from Texas."
The video for the first single, "Come On Over", premiered on Simpson's official website in July 2008. The country album, entitled Do You Know, is scheduled for a September 9, 2008 release.