Kelly Brianne Clarkson was born on April 24, 1982 in Fort Worth, Texas, and grew up in the small town of Burleson, Texas. She is the third and youngest child of Jeanne Ann Rose, a first grade teacher who is of Greek and Irish descent, and Stephen Michael Clarkson, a former engineer who is of Welsh extraction. Clarkson's siblings include her brother Jason, and her sister Alyssa. When Clarkson was six years old, her parents split up 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. Clarkson frequently moved around Texas while her mother managed several professions in order to support the family. Clarkson has since stated that, being six years old at the time, she did not understand why her family had been constantly moving. Eventually, the family settled in Burleson, where Clarkson's mother married her second husband, Jimmy Taylor.

Clarkson attended Fulton Middle School and Burleson High School. She originally wanted to become a marine biologist but decided against it after seeing "Jaws." In seventh grade, a teacher [Cindy Glenn] overheard her singing in a hallway and asked her to audition for the school choir. Clarkson told the teacher that she had never received professional vocal training before. In high school, Clarkson performed in musicals such as Brigadoon.

Upon graduation in 2000, Clarkson worked several occupations to finance her demo CD that she hoped to market toward record labels. She received few responses, and eventually decided to move to Hollywood to seek out other opportunities in music, one of which was a mentorship under songwriter Gerry Goffin. However, Goffin fell ill, and to make ends meet, Clarkson appeared as an extra on Sabrina, the Teenage Witch and That '80s Show among others. She played a small role in the 2002 film Issues 101. Following four months in Hollywood, Clarkson was discouraged when her apartment burnt down and decided to return to Texas, where she worked at a cinema, and as a cocktail waitress, Six Flags performer, telemarketer, Kirby Vacuum salesperson, and a Red Bull promoter.

Once Clarkson returned to Burleson, several of her friends encouraged her to audition for the 2002 debut of the reality television program American Idol. She entered the competition with 10,000 others, and the judges Paula Abdul, Simon Cowell and Randy Jackson were impressed with her voice. She earned a position in the Top 30 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 10 position. Other songs Clarkson performed on American Idol include Carole King's "(You Make Me Feel Like) A Natural Woman", Badfinger'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 and earned 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 debut 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-standing 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.; it spent five weeks at number one in Canada, and remains Clarkson's only #1 there.

Shortly following the completion of the first season of American Idol, Clarkson was accused of working with a record company. American Idol's rules stated that a contestant was not allowed to compete on the program if they had been linked to a record company. However, she was cleared of all allegations, as she had only had a contract in order to conduct demonstration work.

Soon after winning American Idol, Clarkson starred with Idol runner-up Justin Guarini in the movie From Justin to Kelly. The film was poorly received by critics and grossed only $5 million at the North American box office, less than half its reported budget. Clarkson has not taken any acting roles since, and says she is shocked when people send her scripts after From Justin to Kelly, often citing contractual obligation as her sole reason for involvement in the film.

Clarkson is the only American Idol winner so far who has not held the title for an entire year, since season 2 started the following spring.

In December 2003, a competition titled World Idol was held in London, England, gathering the winners of the first seasons of Idol from across the globe. Clarkson placed second behind Norwegian Idol Kurt Nilsen. She performed Aretha Franklin's "(You Make Me Feel Like) a Natural Woman". Because she left immediately after the competition, she was chided by some in the media for what they saw as poor sportsmanship. Clarkson later explained to fans that she was suffering from illness.

Kelly is a two-time Grammy award winner and is a multi-platinum artist. Thankful went Double Platinum selling 3 million copies while her second album, Breakaway went 6x platinum selling 11 million copies.

On Christmas Day, 2006, American Top 40 radio show Host Ryan Seacrest announced during a countdown of 2006's most popular songs, that Clarkson has had a song in the Top 40 for the past 111 weeks, making her "the most successful female artist in AT40 history", according to Seacrest.