Anastacia was born Anastacia Lyn Newkirk in September 1968 in Chicago, Illinois, where her late father, Robert Newkirk (of German descent) was a club-singer and her mother, Diane Hurley (of Irish descent), was an actress in musical theatre. Her father left the Newkirk family when she was a teenager, and the family moved to New York City, where Anastacia enrolled at the Professional Children's School in Manhattan. Despite being diagnosed with Crohn’s disease when she was 13, Anastacia soon became interested in dance, and gained prominence by singing Oleta Adams' "Get Here" on “Comic View” in 1992. Throughout the early 1990s, Anastacia appeared regularly on Club MTV, and in a couple of videos for the female hip hop group Salt-n-Pepa.
In 1999, she attracted the interest of record labels after making the finals of MTV talent show “The Cut”, hosted by the late Lisa "Left Eye" Lopes of the girl group TLC. Anastacia finished in 2nd place, but impressed Lopes and the show's 3 judges enough to earn a record deal, signing a contract with Daylight Records (a custom label of Sony BMG's Epic Records) in March 1999.

Debut album, ”Not That Kind”, was released in June 2000, reaching the Top 10 in 8 countries in Europe, Asia, and Oceania, and going triple platinum in Australia. Debut single "I'm Outta Love" topped the charts in Australia and New Zealand, made number 2 in France, number 6 in both the UK and Germany, and the Top 10 on the Hot Dance Club Play chart. Second single "Not That Kind" reached number 11 in the UK, made the Top 10 in Italy, and the Top 20 in Switzerland and France. “Cowboys & Kisses" was the third single off the album, but this enjoyed modest success compared to its 2 predecessors, only charting in the Top 40 in some European countries. The final single from the album, "Made for Lovin' You" charted at number 27 in the UK, and number 72 in France.

Anastacia’s second album, ”Freak of Nature”, released in November 2001 and dedicated to the late Lisa “Left Eye” Lopes who had a huge influence on her career, achieved respectable sales, but didn’t match the level of international success of ”Not That Kind” (the album’s title was derived from a nickname her mother gave to her). The first single released was "Paid My Dues", followed by "One Day in Your Life", which reached number 11 in the UK and the Top 10 in many European countries. Next single "Why'd You Lie to Me" made the Top 30 in the UK, and fourth single "You'll Never Be Alone" reached number 28 on the Adult Contemporary chart in the US. She also contributed the song "Love Is a Crime" to the “Chicago” soundtrack, a song which peaked at number 1 on the Hot Dance Club Play chart.

In January 2003, Anastacia discovered she had breast cancer. She immediately started and successfully completed surgery and radiotherapy, subsequently establishing the Anastacia Fund to promote awareness of breast cancer among younger women. She has attributed this health scare to being an inspiration for the sound and content of her self titled third album, which she began recording in September 2003, working with Glen Ballard, Dallas Austin and David A. Stewart. ”Anastacia”, released in March 2004, reached the top of the album charts in the UK (on 2 separate occasions), Ireland, the Netherlands, Australia, Greece, and Germany and number 2 in Italy, Spain and Portugal. However, unlike her first 2 albums, it wasn’t released in her homeland. First single, “Left Outside Alone" proved equally successful, reaching number 1 in Australia, Spain, Italy, Austria and Switzerland; number 2 in the Netherlands and Germany and number 3 in the UK. In the US, the dance mix of "Left Outside Alone" peaked at number 5 on the Hot Dance Club Play chart. 3 further singles were released from the album, "Sick and Tired", providing another Spanish number 1 and another Top 5 spot in the UK, "Welcome to My Truth" (her best-selling hit in Spain), and the ballad "Heavy on My Heart", the sale proceeds from which went towards the Anastacia Fund. On the album, Anastacia also collaborated with P.O.D. lead singer Sonny Sandoval on the socially conscious track "I Do".

In November 2005, Anastacia released her first greatest hits collection, called ”Pieces of a Dream” (named after a track on the album), which included the single "I Belong to You (Il Ritmo Della Passione)", a duet with Eros Ramazzotti which made the Top 10 in almost all European countries.

Fourth studio album, “Heavy Rotation”, was released in October 2008 in Europe and Asia (and elsewhere in 2009). The new album features collaborations with producers Ne-Yo, The Heavyweights, Lester Mendez, J.R. Rotem, and Rodney Jerkins. The album's first single was "I Can Feel You", followed by "Absolutely Positively", which served as a promotional single. The second official single was "Defeated".

Anastacia has sold over 20 million albums worldwide.