Kelly Brianne Clarkson was born in Fort Worth, Texas and grew up in the small town of Burleson, Texas, a suburb of Fort Worth. She is the third and youngest child of Jeanne Rose, a first grade teacher, and Stephen Michael Clarkson, a former engineer. She is of part Greek ancestry. 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. As a result, 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. The family settled in Burleson, where Clarkson's mother married her second husband, Jimmy Taylor.

Clarkson's family struggled financially, and music became her refuge after the first divorce. Clarkson attended Pauline G Hughes Middle School and Burleson High School, originally aiming to become a marine biologist. In seventh grade, a teacher (Mrs. Cynthia 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. In high school, Clarkson performed in musicals such as Annie Get Your Gun, Seven Brides for Seven Brothers and Brigadoon. Around this time, Clarkson decided to pursue singing. She sang at her high school talent show, after which a gentleman shared some inspiring words with her: "God has given you this gift. You've got to sing. You're destined to sing." Clarkson did continue to sing and soon started classical training, hoping that music would be her ticket to a college scholarship.

Clarkson worked numerous odd jobs during and after high school, such as mowing lawns, helping her contractor stepfather build porches, and working in a movie theater starting at age 16 and until she moved to Los Angeles. She also worked for Papa John's, Subway, Six Flags Over Texas, Starbucks, and sold vacuums door to door (her latter experience which she described with a well-intended pun: "It sucked."). She attended Crestmont Baptist Church in Burleson during her high school years.

Upon high school graduation, Clarkson was offered full scholarships to The University of Texas at Austin, University of North Texas, and Berklee, but decided against college because she had "already written so much music and wanted to try on own. And figured you're never too old to go to college."

Clarkson won the first season of American Idol on September 4, 2002, earning 58% of the vote to 42% for 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 at Pantages Theater in Hollywood, and incorporated short scenes of Clarkson performing on Idol. When released as a single in October 2002, it set a record on the U.S. Billboard Hot 100 chart when it rose from number 52 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.

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 mentioned in interviews that 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.

In December 2003, a competition titled World Idol was held in London, UK, gathering the winners of the first seasons of Idol from across the globe. Clarkson was contractually obligated to participate, and 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 an illness.

Following the successful release of "A Moment Like This", Clarkson's full-length debut album Thankful was released in North America by RCA Records on April 15, 2003. It debuted at number one on the U.S. Billboard 200. Eventually, the album was certified double platinum by the RIAA for sales of two million copies on December 8, 2003 and platinum by the CRIA for sales of 100,000 copies on February 10, 2004. Reviews for the album were generally favorable. However, several critics noted that her early achievement was established due to her performances on American Idol. Allmusic critic Stephen Thomas Erlewine praised the album for its vocal ability: "throughout this record, 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 criticized 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". 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 33 on the Australian albums chart. Further singles released outside North America would appear even less successful.

"Low", the third single from Thankful, reached number two in Canada, but it was unable to make the Top 40 of the U.S. chart. The final single, "The Trouble with Love Is", was not released in Canada, and it peaked at #101 on the U.S. Charts. Clarkson attributed the under performance of both releases to poor management and relieved her manager Simon Fuller, who she felt was not completely focused on her career. Clarkson also covered Danielle Brisebois' "Just Missed the Train" on the album.

Distancing herself from her American Idol image, Clarkson took more creative control with her second studio album Breakaway, and developed a more rock-oriented image. Breakaway was released by RCA Records on November 30, 2004. The album debuted within the U.S. top five and Canadian top ten, but sales were initially low in comparison to Thankful. However, the single releases from Breakaway proved very successful, and allowed it to become only the fourth album in history to stay in the Billboard 200 Top 20 for a consecutive year, as well as, being certified 6x platinum in the U.S. in late 2007 and 5x platinum in Canada in May, 2006. In Australia, the album reached number two and spent 52 weeks in the top 10 and was certified 6x Platinum; however, it experienced a delayed release in the UK. Clarkson co-wrote six of the songs with several songwriters, such as former Evanescence band members Ben Moody, David Hodges and producer Max Martin; the title track was co-written by punk-pop singer Avril Lavigne. Breakaway received different responses from critics; Rolling Stone commented that "on Kelly Clarkson's second album, she embraces her rock side rather than the pop pageantry that put her on top of the American Idol heap". TeenInk noted the strength of her vocals on Breakaway, and praised the change from pop music to contemporary rock: " retains the incredible power and beauty of her voice while switching to rock". Stylus magazine also enjoyed Clarkson's foray into rock music, however, she was called out because of her American Idol image, which reviewer Charles Merwin believed she had yet to lose. He praised the non-singles and wrote that they "maintain a quality high". Allmusic called the album "a nice, low-key relief".

Clarkson appeared on numerous television programs during the promotional tour for Breakaway, some of which included Saturday Night Live, The Oprah Winfrey Show and The View; she performed the first two singles "Breakaway" and "Since U Been Gone" on Saturday Night Live, which became her first major telecast appearance in order to support the album. "Breakaway", co-written by Avril Lavigne, served as the original song for The Princess Diaries 2: Royal Engagement (2004) and achieved considerable success across the world; it became Clarkson's third top-ten single in the U.S. and fourth top-ten single in Canada. It reached number ten in Australia, and number 22 in the UK. The song's contemporary pop-rock ambiance was one of the several tracks including a stronger rock-influenced sound that had not been heard on Thankful. The second single "Since U Been Gone", which was 'produced' by Max Martin, became the most successful release from the album. Its music video presented Clarkson singing to an underground audience with a full band; cut scenes of Clarkson destroying a former boyfriend's apartment were incorporated. The song's strong rock ambiance allowed it to reach number two in the U.S. and the top five across the world. It also earned Clarkson her first Grammy Award for "Best Female Pop Vocal Performance"; she won a second award for "Best Pop Vocal Album".

The third and fourth single releases, "Behind These Hazel Eyes" and "Because of You", also followed with chart success. The video for "Behind These Hazel Eyes" broke the record for days at #1 for a female artist with 33 out of 50 days #1 on TRL. "Because Of You" became Clarkson's biggest worldwide hit, her first to reach the number one position on the world chart show, where it held for two consecutive weeks in 2006. The video for "Because of You" won the 2006 MTV Video Music Award for Best Female Video, her second consecutive win in that category (The first being from "Since U Been Gone"). The fifth single from Breakaway, "Walk Away", was a top 15 hit in the U.S. and a top five hit in Canada. Breakaway spent 103 weeks on the Billboard 200. It fell out of the Billboard 200 in late November and was moved to Billboard's Pop Catalog. Breakaway was the tenth best selling album of 2006 in the US, adding nearly 2 million additional sales to the 2005 and 2004 sales. As a testament to Clarkson's continuing popularity, she was the most-played artist of 2006 on American radio, despite releasing only one single in the entire year, "Walk Away". On December 23, 2006, American Top 40 radio show host Ryan Seacrest announced during a countdown of 2006's most popular songs that Clarkson had had a song in the American Top 40 for 111 weeks, making her "the most successful female artist in AT40 history". She was also the most radio broadcasted artist of 2006 in Australia and "Because Of You" was the third most broadcast song of the same year, despite being released in 2005.

In the summer of 2006, Clarkson lent Ford Motor Co. a song titled "Go", written by Clarkson and Rhett Lawrence ("Miss Independent"). The song is being used in the company's new advertising campaign, "Bold Moves".

As of 2009, Breakaway has sold over 13 million copies worldwide.

While on tour in Europe in 2006, Clarkson began writing and composing songs for her third album, My December. During the Addicted Tour, Clarkson debuted two of her songs: "Maybe" and "Yeah". Recording commenced on the album in the summer of 2006. The first single from My December was "Never Again", which made its radio debut on April 13, 2007. The song was released on iTunes on April 20, 2007, but was taken down and replaced with a notice that said that the song was not available until April 23, 2007. The single peaked on the Billboard Hot 100 at #8 and on the Pop 100 at #5. Following "Never Again", Clarkson released "Sober" as her next single from My December on June 6, 2007. The singles were promoted with appearances on Good Morning America and The Tonight Show with Jay Leno. Clarkson also returned to American Idol on the May 23, 2007 season 6 finale for the first time since its third season, performing "Never Again" and "Sgt. Pepper's Lonely Hearts Club Band" with Aerosmith guitarist Joe Perry during a Beatles medley. The song "Chivas" is a hidden track which can be found after the song "Irvine." Clarkson wrote the song on bar napkins before going to a concert by Los Angeles based cover band Metal Skool where she was famously seen sharing a bottle of Chivas Regal with Ryan Key of Yellowcard in a popular YouTube video when she was brought on stage to sing with the band.

Clarkson parted with her management, The Firm, on June 11, 2007, after the controversy surrounding My December.Clarkson would then sign with Starstruck Entertainment, run by Narvel Blackstock - the husband of Reba McEntire - on July 2, 2007. On June 14, 2007, Live Nation announced that Clarkson's summer tour—her first nationwide arena tour—had been canceled due to underwhelming ticket sales, to be rescheduled after the release of the My December album at smaller, more intimate concert environments. Clarkson reinstated plans to tour the US during 2007, with a much smaller tour than the one she canceled in June. Clarkson began her My December Tour on October 10 in Verona, New York in venues significantly smaller than those previously booked.

My December was officially released in the U.S. on June 26, 2007. On the date of the album's release, Clarkson appeared on Good Morning America to promote her new album. Clarkson performed songs from this new album, including the single "Never Again". Despite the controversy surrounding My December, the album debuted at #2 in the U.S. with 291,000 albums sold.This is a slightly higher debut than Clarkson's previous album, Breakaway, which debuted at #3.

On July 7, 2007, Clarkson performed on the American leg of Live Earth. Her five-set performance list included: "Walk Away", "How I Feel", "Never Again", "Sober", and "Since U Been Gone".

Clarkson was the celebrity coach for Canadian Idol during its Top 5 week of the fifth season, aired on the CTV network on August 20, and she performed on the results show the next night.She was also awarded a Platinum Certification for shipments of more than 100,000 copies of My December in Canada. Clarkson also performed at the 2007 NFL opening kickoff where she sang the national anthem and performed songs from My December including "Never Again", "Maybe" and "Don't Waste Your Time". Clarkson also performed in the halftime show for the Dallas Cowboys and New York Jets game on Thanksgiving Day.

My December was certified both gold (500,000 copies shipped) and platinum (1,000,000 copies shipped) on December 12, 2007, by the RIAA.It has sold over 2.5 million copies worldwide.

On April 19, 2008, Clarkson participated in a Papal Youth Rally at the campus of St. Joseph's Seminary, Dunwoodie in Yonkers, New York performing a mini-concert for those in attendance. This was the Papal Visit of Pope Benedict XVI. She performed Schubert's "Ave Maria" for the Pope later in the day following the Pope's speech. Clarkson, raised Baptist, was said to be honored by the invitation and appreciative of the rosary given to her and her band by the Pope, who were invited over by the Pope immediately following the performance for the rosary honor.

Clarkson's fourth album, All I Ever Wanted, was released March 10, 2009. During recording of the album, Clarkson worked closely with producer-songwriters Ryan Tedder, Dr. Luke, Max Martin, and Howard Benson, among others. The album’s recording was completed on October 23, 2008. The first single off the album, "My Life Would Suck Without You", was sent to radio on January 13, 2009, and was available to download thereafter. The single first entered the Billboard Hot 100 at #97. The following week, the single shot to #1, breaking the record of largest leap to the top spot, formerly held by Britney Spears' "Womanizer" This marks the second time Clarkson has broken the record, her first being the American Idol victory ballad "A Moment Like This", which shot from #52 to #1 in 2002. In March 2009, Kelly reached #1 in the UK singles chart with 'My Life Would Suck Without You'. This is Kelly's first UK #1 single. In its first week of sales, it moved 255,000 copies in the USA, and debuted at number 1 on the Billboard 200, the album sold 90,000 copies in its second week and remained at #1. The album's second single has been confirmed to be "I Do Not Hook Up".