Clarkson was born in Fort Worth, Texas on April 24, 1982. She is the third and youngest child of Jeanne Ann Taylor, a first grade English teacher of Greek descent, and Stephen Michael Clarkson, a former engineer of Welsh extraction. Clarkson's siblings include her older brother Jason, and her older sister Alyssa. When Clarkson was six years old, her parents separated after seventeen years of marriage; her brother went to live with her father, her sister went to live with an aunt, and Clarkson remained with her mother. Following the separation, Clarkson frequently moved around Texas while their mother managed several occupations in order to support the family. Being six-years-old at the time, Clarkson did not understand why her family had been constantly moving and said that children usually do not comprehend the process of divorce. Eventually, the family settled in Burleson, Texas and Clarkson's mother subsequently remarried to Jimmy Taylor.
Clarkson attended Pauline Hughes Middle School when she reached seventh grade. She had originally wanted to become a marine biologist, but during the same school year, a teacher overheard her singing in a restroom and asked her to audition for the school choir. Clarkson told the teacher that she had never received professional vocal training before. She attended Burleson High School following middle school and began performing in musicals such as Brigadoon.
Upon graduation, Clarkson worked several occupations to finance her demo CD that she had been hoping to market toward record labels. She received few responses though, and she eventually decided to move to Hollywood to seek out other opportunities in music. However, early attempts went unnoticed and Clarkson wound up appearing as an extra on Sabrina, the Teenage Witch to make ends-meet. After her apartment was burned down in a fire, disappointed, she returned to Texas. In order to make a living, Clarkson worked at a cinema, as a cocktail waitress, telemarketer, and a Red Bull promoter.
Upon returning to Burleson, many of Clarkson's friends encouraged her to audition for the 2002 début of the reality television program American Idol. Entering the competition alongside ten thousand others, the judges Paula Abdul, Simon Cowell and Randy Jackson were impressed with her voice. She earned a position in the top thirty finalists and week-by-week, performed a song on live television to North America. When American Idol concluded each week, the viewers would vote based on the performance they enjoyed the most. Clarkson sang a rendition of Aretha Franklin's "Respect" which garnered her a top ten position. Other songs Clarkson performed on American Idol include Aretha Franklin's "(You Make Me Feel Like) a Natural Woman", Mariah Carey's "Without You", and Céline Dion's "I Surrender".
Clarkson had made it to the final two contestants on American Idol, and on September 4, 2002, she won the competition, earning 58% of the audience vote over Justin Guarini. Choking back tears, Clarkson performed the ballad "A Moment Like This", the song written for the winner of American Idol, which would subsequently appear on her début album Thankful. The song's music video was filmed in an abandoned theatre and incorporated short scenes of Clarkson performing on Idol. When released as a single in October 2002, it set a still-record on the U.S. Billboard Hot 100 chart when it rose from number fifty-two to number one. This achievement was largely due to the impact from Idol as the CD single managed to sell 236,000 copies in its first week of sales in the U.S.; the single spent five weeks at number one in Canada.
Following the successful release of "A Moment Like This", Kelly Clarkson's début full-length album Thankful was released in North America by RCA Records on April 15, 2003. It debuted at number one on both the U.S. Billboard 200 and Canadian albums chart. Eventually, the album was certified double platinum by the U.S. RIAA for sales of two million copies on December 8, 2003 and platinum by the Canadian CRIA for sales of 100,000 copies on February 10, 2004. Reviews for the album were generally favorable, however, several critics noted that her success was largely because of American Idol. All Music Guide critic Stephen Thomas Erlewine praised the album for its vocal ability: "throughout this record, [Clarkson] makes it seem effortless and charming. She can croon, she can belt out a song, she can be sexy and sassy while still being graceful and as wholesome as the girl next door". Rachel Kipp of JS Online criticised Clarkson for not having the same personality on Thankful that she had on American Idol, and wrote: "on American Idol, Clarkson showcased a great voice and an endearing, "aw-shucks" personality. That personality is missing on Thankful, and there lies the album's greatest fault". Kipp blamed the producers behind the album for not allowing Clarkson to be herself.
"Miss Independent" became a success when released as the second single from Thankful. It reached the top ten of the U.S. and Canadian singles charts, and earned Clarkson a 2004 Grammy Award nomination for "Best Female Pop Vocal Performance". She failed to win the award though. When the single was released in the United Kingdom and Australia, it reached the top ten of the charts, however, Thankful received less attention. It peaked at number forty-one on the UK albums chart and at number thirty-three Australian albums chart. Further singles released outside North America would appear even less successful.
The third single taken from Thankful "Low" reached number two in Canada, however, was unable to reach the top fifty of the U.S. chart. "The Trouble with Love Is" yielded low peak positions on both charts which lead critics to categorizing Clarkson as an American Idol has-been. Clarkson spent much of the end of 2003 and the beginning of 2004 out of the limelight while writing her second album.
In the summer of 2004, Clarkson returned to the music industry with the single "Breakaway", from the film The Princess Diaries 2: Royal Engagement, which became her biggest hit in the U.S. since her debut single. It preceded Clarkson's pop rock, Adult contemporary and rock and roll–influenced second album, Breakaway, released in the U.S. on November 30, 2004. Clarkson, who co-wrote over half of the album's tracks with songwriters and producers such as Max Martin, singer Avril Lavigne, and former Evanescence band members Ben Moody and David Hodges, categorized the album as being in the pop rock genre, unlike Thankful. Breakaway received praise from critics, who noted its harder, more rock and roll-flavored edge, one that invited comparisons to Avril Lavigne. In an effort to promote her new album, Kelly blanketed the airways with performances of The Tonight Show, The View and Saturday Night Live. Breakaway (the album) received a fifth U.S. platinum certification (five million shipped) in January 2006 and was 2005's third best-selling album. It became her first platinum album in the UK (later receiving the triple platinum award and selling over a million copies) and was also was certified quadruple platinum in Canada and six times platinum in Australia. In Indonesia, she is the 2nd artist, after Britney Spears, in Indonesian chart history to have four number-one singles from the same album. Breakaway spent 61 weeks in the top 20, becoming only the 4th album to spend over a year in the top 20 in SoundScan history. Clarkson was named by Teen People magazine as one of the "Hottest 25 Stars Under 25". On 8 February 2006 Clarkson received two Grammy Awards: one for best pop vocal performance ("Since U Been Gone") and one for Best Pop Vocal Album. She performed the song "Because of You".
The album's second single "Since U Been Gone" peaked at number two on the U.S. Hot 100 (and was successful on the majority of Billboard formats), was a top five single in the UK and reached number one in Canada. It has become Clarkson's biggest hit to date and one of the biggest singles of 2005, was nominated for the Record of the Year award in the UK, and won the Grammy Award for Best Female Pop Vocal Performance. In the Village Voice annual critics poll, it placed third on a list of the year's best singles" and "Because of You" both reached the U.S. top ten and the Canadian top five, and the latter was one of the most requested songs on teen radio in 2005. With "Because of You," Clarkson became the first pop artist since Beyonce to have four top-ten hits from the same album. In Canada, Clarkson became one of the few international artists. Blender magazine named it the #1 song of 2005.