Coyle was born on 15 June 1985 to Lillian and Niall Coyle in Derry, Northern Ireland. Her parents first noticed her talent for singing at the age of two, when she sang The Drifters' "Saturday Night at the Movies." Coyle was uninterested in her education but received good grades. She recorded a demo CD, which was distributed to Louis Walsh and The Late Late Show. The CD included cover versions of "Fields of Gold", "Somewhere Over the Rainbow", "Love Is", and the aria "Summertime".
While attending Thornhill College in 2001, Coyle auditioned for the Irish version of the reality television talent show Popstars, on which Louis Walsh was a judge. She won a place in the band Six, but it was later revealed that she had lied about her age. She was just 16 years old, two years younger than the minimum age requirement of 18. Coyle said she was "exploited" by RTÉ. She returned to Thornhill College in Derry. She later revealed how she had a cancer scare when she found a lump in her breast when she was 17.
Walsh encouraged Coyle to enter Popstars: The Rivals, the second British series of the international Popstars franchise. The series' goal was to create two winning pop groups – a boy band and a girl group, each consisting of five members who would then partake in "a battle of the sexes" as they vie for the Christmas number one on the UK Singles Chart. Several thousand applicants attended auditions across the UK in hope of being selected. Ten girls and ten boys were chosen as finalists by judges Walsh, Pete Waterman, and Geri Halliwell. These finalists then took to the stage participating in weekly Saturday night live performances (alternating weekly between the girls and boys). Following her performance of "Fields of Gold", Walsh told her she gave the "performance of the night. Stole the show for me," while fellow judge Halliwell said, "I'd love to buy a single of yours already".
Coyle joined Cheryl Tweedy, Sarah Harding, Nicola Roberts, and Kimberley Walsh to comprise the new girl group Girls Aloud, formed through the show by a public vote on 30 November 2002. The group's debut single "Sound of the Underground" peaked at number one on the UK Singles Chart, becoming the 2002 Christmas number one. Girls Aloud hold the record for the shortest time between formation and reaching number one. The group released their debut album Sound of the Underground in May 2003, which entered the charts at number two and was certified platinum by the British Phonographic Industry (BPI) later the same year. Their singles "I'll Stand by You", "Walk This Way", and "The Promise" have charted at number one. Two of their albums have reached the top of the UK Albums Chart: their greatest hits album The Sound of Girls Aloud and 2008's Out of Control, both of which entered the chart at number one, with over one million copies of the former being sold. They also achieved seven certified albums and have been nominated for five Brit Awards, winning the 2009 Best Single for "The Promise".
The group's musical style is pop, but throughout their career they had experimented with electropop and dance-pop. Girls Aloud's collaborations with Brian Higgins and his songwriting and production team Xenomania earned the group critical acclaim, due to an innovative approach to mainstream pop music. The group became one of the few UK reality television acts to achieve continued success, amassing a fortune of £30 million by May 2010. Guinness World Records lists them as "Most Successful Reality TV Group" in the 2007 edition. They also hold the record for "Most Consecutive Top Ten Entries in the UK by a Female Group" in the 2008 edition, and are credited again for "Most Successful Reality TV Group" in the 2011 edition. The group was also named the United Kingdom's biggest selling girl group of the 21st century, with over 4.3 million singles sales and 4 million albums sold in the UK alone.
In 2009, Girls Aloud decided they would partake in a hiatus to pursue solo projects.
In March 2010, Coyle made her first solo appearance, singing "Love Me for a Reason" with Boyzone on a televised tribute to the late Stephen Gately. She collaborated with Boyz II Men for their album Love, recording a cover of the Take That song "Back for Good", although the song was cut from the final track listing. Coyle also worked with Jay Sean, although the duet was later scrapped.
Coyle announced plans to release a solo album during Girls Aloud's hiatus. She enlisted Barbara Charone, who has worked with Madonna and Christina Aguilera, as a publicist and Bruce Garfield as her manager. Despite early reports indicating three major record labels interested in Coyle, it was reported that Coyle had failed to earn a solo record deal, even being turned down by Girls Aloud's label Polydor Records. In April 2010, it was reported she had signed to Geffen Records. The deal later fell through. In August 2010, Coyle officially signed a deal with grocery store chain Tesco's new record label, releasing the album through her own Black Pen Records imprint.
Coyle released her debut album Insatiable on 8 November 2010. She worked with a number of famous songwriters and producers during recording sessions, such as Desmond Child, Guy Chambers, Mike Elizondo, Steve Booker, Toby Gad, Tony Kanal and newcomer Ricci Riccardi. Coyle also worked with Lucie Silvas, Matchbox Twenty's Kyle Cook, William Orbit, and Tiesto. According to an interview with Booker, Coyle had worked on song ideas using GarageBand which she then presented to Booker in England to work on together further. The producer said, "She was singing her songs to loops, and then I took the loops out and rewrote the music from scratch to her ideas." He described her songs as "very pop". Booker also worked on songs to show off Coyle's vocals: "Because she’s got such a belting voice, I tried a couple of things where she could really belt," he said.
The album was preceded by the release of her debut single, the title track "Insatiable". Co-written with Guy Chambers and produced by Ricci Riccardi, the song has an "80s feel" and "a harder, guitar-led sound." The single peaked at number twenty-six in the UK Singles Chart.
In November 2012, Coyle reunited with the rest of Girls Aloud to celebrate their tenth anniversary. On 18 November 2012, the band released their new single "Something New" which was also the official charity single for Children in Need. The group released their second greatest hits compilation Ten on 26 November 2012. Coyle and the group embarked on the Ten: The Hits Tour in February. After the tour's conclusion in March 2013, the group announced that they were disbanding.
On 4 April 2013, Coyle tweeted that she was back in the studio claiming it was exciting. She stated to Hello! Magazine she has plans to tour around the world and is also working on a TV documentary.
In late June, Coyle appeared on ITV's Michael Flatley: A Night to Remember, as part of ITV Music Specials. On the programme she sang a cover of "Dangerous Games", shortly thereafter she announced she would star alongside Flatley on his 2014 tour on select dates. Coyle, in August, also revealed she has been in the studio recording new songs for her forthcoming second studio album, most likely due in the middle of 2015.
On 16 September 2014, Coyle announced that she began working with longtime collaborator Brian Higgins. In March 2015, Coyle spoke about the details concerning her second album, stating that she intended on signing with a major label and that the sound is "similar" to that of London Grammar.
In July 2017, it was announced that Coyle had signed a recording deal with Virgin EMI Records. She released her new single, "Go to Work", on 8 September 2017.
As a member of Girls Aloud, Coyle has also appeared in the fly on the wall documentary Girls Aloud: Home Truths, the E4 documentary series Girls Aloud: Off the Record, and a one-off variety show entitled The Girls Aloud Party. Coyle has expressed interest in an acting career, following Girls Aloud's cameo appearance as schoolgirls in the film St. Trinian's and Coyle's appearance on Keith Barry's show The Great Escape, which aired on ITV on 29 December 2007. Coyle made a cameo appearance in Natasha Bedingfield's video for "I Wanna Have Your Babies".
Coyle contributed to the book Dreams that Glitter - Our Story, an autobiography with her Girls Aloud bandmates, in October 2008. The book was written with a ghostwriter and published by the Transworld imprint Bantam Press. The book featured unseen photographs and included insights into the members' personal lives, their success together, style tips, and "everything we've learned about life, love and music." The book was previewed and serialised by OK! prior to its release. Girls Aloud held a book signing at Waterstone's in Piccadilly, London to promote the release. The title Dreams that Glitter comes from a line in the group's 2007 single "Call the Shots".
She was reportedly approached by Gillette to advertise their female range of razors. As a member of Girls Aloud, Coyle has also endorsed Barbie, KitKat, Nintendo DS, Samsung, Sunsilk and Pandora.
In December 2009, Coyle visited her hometown of Derry to successfully break the record of the most trees planted in one site in an hour by 100 volunteers. Coyle has also dedicated some of her time to charities, including the Northern Ireland children's hospice.
Coyle published her new record label Black Pen Records, which additionally released her debut album Insatiable and her further singles. In 2012, Coyle served as a guest judge for an episode of the series America's Next Top Model.
After nine years in Los Angeles, Coyle moved back to Northern Ireland to raise her daughter Anaiya . She owns an Irish pub in Sunset Beach, California named Nadine Irish Mist. In 2013, her estimated wealth was £6 million according to that year's Sunday Times Rich List.
In January 2008, Coyle started dating former American football player Jason Bell, and the two were engaged until their split in May 2011. On 15 August 2013, Coyle announced she was expecting a child on her official Instagram account, with the caption: "I'm having a baby Xx". She further confirmed her reunion with ex-fiancé Jason Bell, who is the father of her baby girl. On 10 February 2014, she announced via her Twitter account that the baby had arrived. She introduced baby Anaíya Bell to her Twitter and Instagram followers on 20 April.Note