Burke was born on 25 August 1988 in Islington, London. Her middle names come from her great grandmother (Imelda) and grandfather (Cecil) and her mother's maiden name (Ewan). She is the daughter of Jamaican-born David Burke and British-born Melissa Bell of African-Jamaican, Irish and Dougla descent, who is a former Soul II Soul member. Her parents split up when she was six. She has lived in Islington all of her life and has four brothers and one sister.
Burke started singing when she was five and, prior to The X Factor, had no professional vocal training. At nine years old, she sang on stage in Bahrain with her mother. At the age of twelve, Burke entered the TV talent show Star for a Night where she was the youngest person in the competition. She was beaten to the number-one spot by Joss Stone. At age twelve, she also sang down the phone to Stevie Wonder. When Burke's mother asked her to sing to Jean Carne, Carne was so impressed that she asked her to perform at her show the next night.
Burke attended Elizabeth Garrett Anderson School in Islington and after her GCSEs she left school to pursue a career in music. Before her X Factor success, she had been working as a singer, gigging at weekends in clubs. She also went on tour with "Young Voices", a charity that raises money for children with leukemia, where she performed at large venues such as the Royal Albert Hall.

2005–2008: The X Factor
2005:
Burke auditioned for the second series of The X Factor in 2005 (which was eventually won by Shayne Ward). She made it through to the final seven in Louis Walsh's 16–24 category, effectively the top 21 of the competition; however, Walsh did not choose her for his final four as he felt that she was too young for the competition.
2008:
Burke's second bid to win The X Factor came in 2008. Falling into the "Girls" category, she was mentored by Girls Aloud's Cheryl Cole who selected her for the finals—a series of ten weekly live shows in which contestants are progressively eliminated by public vote. On the first live show, Burke performed Whitney Houston's classic "I Wanna Dance with Somebody". For the second live show she covered "I'll Be There" by The Jackson 5. In week three, big band week, Burke performed Christina Aguilera's "Candyman" and received her first standing ovation. For the disco-themed fourth live show, Burke performed Donna Summer's "On the Radio". During Mariah Carey week on 8 November, Burke and the other finalists met Carey for individual masterclasses, with Carey complimenting Burke on her voice. Burke performed "Without You" and received a standing ovation from the judges who all gave her positive comments. Cowell commented that "by any standard, that was just outstanding". Following the show Burke's performance was also praised by Carey who called her rendition of the song "absolutely amazing".
In weeks 6 and 7, Burke received positive comments from the judging panel for her performances of Joe Cocker's "You Are So Beautiful" and Dan Hartman's "Relight My Fire" (the popularity of which in the UK is mostly a result of Take That's 1993 revival thereof). Week 8 saw her replace Diana Vickers as the bookies' favourite after performing Britney Spears' "Toxic" and Beyoncé Knowles' "Listen", for which she received yet another standing ovation. In week 9, Burke performed Rihanna's hit song "Don't Stop the Music" and again received positive comments, with Louis calling her "the British Beyoncé" and Simon commenting "...We may be seeing the birth of a star here [...] you've got it all, that was a terrific performance". Diana Vickers was eliminated in the semi-final, to the shock and upset of both Burke and Eoghan Quigg. Burke confessed after Vickers' final performance that she thought Vickers was going to win.
Burke was joined in the grand final by Irish teenager Eoghan Quigg and boyband JLS. She sang "Listen" as a duet with Beyoncé (who later performed her UK number-one single "If I Were a Boy"), and after performing with the American singer she proclaimed: "I have achieved a dream".
"Hallelujah"
After the elimination of Quigg she sang what would become her debut single, a 1984 song by Leonard Cohen, "Hallelujah", for the first time. Finally, with over eight million votes cast in total, Burke was revealed as the winner with 58% of the final vote. The single went on to become the Christmas number one of 2008, holding the top spot for three weeks and selling one million copies. There was also a campaign to take Jeff Buckley's cover of "Hallelujah" to the top of the Christmas chart to deny Burke the top spot. The campaign was fuelled by Jeff Buckley fans' dislike of The X Factor's commercialism and the song's arrangement, as well as a desire by this contingent to introduce younger music fans to Buckley's version. Burke herself was not enamoured of the choice of song, remarking "It just didn’t do anything for me"

On 13 February 2009 it was reported that Burke signed a £3.5 million, five-album US record deal with Epic Records.
Burke's first album was originally scheduled for March 2009 however, Simon Cowell confirmed that her album was scheduled for release later in the year to allow Burke to polish her skills and find the right songs for the album and that it would not be rushed, as previously happened with Leona Lewis' debut album. The album was released on 19 October 2009 in the UK, titled Overcome.
Burke's first commercial single from her debut album is titled "Bad Boys". The single featuring Flo Rida premiered in the UK on The Chris Moyles Show on BBC Radio 1 on 25 August 2009.On 18 October 2009 Bad Boys topped the UK singles chart.
After visiting Burke in the studio, Beyoncé spoke of possibly recording a duet with Burke and also for Burke to join her for Beyonce's second European leg of her I Am… Tour.
American rapper 50 Cent has expressed an interest in Burke, correctly predicting that she would win The X Factor and invited her to appear in an upcoming music video of his, most likely for a song from his upcoming album Before I Self Destruct.
On 19 July 2009, Burke confirmed that she had signed a six figure contract with Italian fashion designers Dolce & Gabbana, to become the face of a new fashion line. She will also model their clothes and accessories in her music videos.
Burke performed on the Royal Variety Show on 7 December 2009.
It was confirmed by Burke on 17 November 2009, that "Broken Heels" will be the 2nd commercial single, (3rd overall), from Overcome. She also confirmed via her Official Twitter page that the video was shot in Los Angeles on 22 and 23 November 2009. The single is set to be released on the 18 January 2010. Burke appeared on the The Paul O'Grady Show on 3 November 2009 to perform "The Silence". She performed on penultimate episode on 17 December 2009 singing "Broken Heels".
It was confirmed on 31 December 2009 that "Hallelujah" is the 5th and "Bad Boys" is the 68th biggest selling singles of the Decade. "Bad Boys" is the 8th biggest selling single of 2009.
Hallelujah is the 6th biggest selling single of the decade in Ireland.

Alexandra Burke has recently signed a five album £3.5 million recording deal with Epic Records, which is expected to give her international fame. She will go on a US promotional tour and then will release her music in the USA.
Burke has recently said, 'I'm really looking forward to it, but at the same time extremely nervous and scared because it's a whole new world. It was all because of Beyonce. She rang up people and was like "You need to watch this girl"'.