Leroy's parents left Saint-Renan (Finistere) when she was four years old. After living in Paris, Lille, and Guingamp, her mother, Muriel Leroy, and her younger sister, Kay, settled with Leroy's grandparents in Saint-Yorre. Her mother divorced from her father, professional footballer Jean-Luc Le Magueresse, in 1993.
Nolwenn studied at the "College des Celestins" in Vichy. When Leroy was eleven, her music teacher noticed her musical talents and encouraged her to learn the violin. At the age of thirteen she won "Les ecoles du desert", a contest sponsored by the Cora supermarket chain, which allowed her to travel with a humanitarian mission from Gao to Timbuktu, Mali; she later claimed this had a profound influence on her.
In July 1998, Leroy was awarded a scholarship by the Vichy Rotary Club to travel to Hamilton, Ohio, as an exchange student. While attending Hamilton High School, she took music lessons at the Performing Arts School and became fluent in English during her stay there. When she returned to France, she began classical singing classes at the Vichy music conservatory. In 2001, she enrolled in the University of Clermont-Ferrand to study law for a potential alternative career to music.
After watching the first series of Star Academy broadcast on TF1 in 2001, Leroy was impressed by Armande Altai, a singing teacher and one of the show's judges, and decided to join Altai's singing classes in Paris for over six months. In 2002, Nolwenn was selected for the second season of the show, but she was also given the part of Scarlett O'Hara in the French stage musical Autant en emporte le vent (Gone with the Wind) by Gerard Presgurvic. Leroy finally chose the television singing competition over the musical and joined the Dammarie-les-Lys castle in late August 2002, where she followed acting, dancing and singing classes for four months. She was declared the overall winner, ahead of her fellow finalist, Houcine Camara, on 21 December 2002.
Leroy's first album, Nolwenn, was released in March 2003 and was certified platinum by November for sales exceeding 300,000 copies. In 2006, the album was certified two times platinum by the Syndicat national de l'edition phonographique (SNEP) for more than 600,000 copies sold. Four songs from the album, "Casse", "Une Femme cachee", "Suivre une etoile" and "Inevitablement" were released as singles. Leroy went on tour in France, Belgium and Switzerland in late 2003 to promote songs from the album.
Leroy's second album, Histoires Naturelles, was produced by Laurent Voulzy and Frank Eulry. Five singles were released from the album. "Nolwenn Ohwo!", co-written by Alain Souchon, Voulzy and Leroy herself, topped the French music charts. The second single was the title track, "Histoire Naturelle". Music videos were made for both songs; the video for "Histoire Naturelle" expressed the main theme of the album with Leroy being portrayed as natural history museum exhibits. Of the other single releases, "Mon Ange" was distributed digitally while "J'aimais tant l'aimer" and "Reste Encore" were promotional-only. The album reached platinum status with 400,000 copies sold. Songs from Histoires Naturelles and Nolwenn were performed on Leroy's second tour entitled "Histoires Naturelles Tour", which started in September 2006. Leroy's first live album was subsequently released in late October 2007.
Le Cheshire Cat & Moi was a project that began in 2007, co-written by Leroy and Teitur Lassen, with contributions from Jonatha Brooke, Michelle Featherstone, Mike Errico and Rupert Hine. It was arranged and produced by Lassen, and recorded in Sweden and the Faroe Islands. The album's lead single, "Faut-il, faut-il pas ?", was released in November 2009 along with a music video directed by Yoann Lemoine. Leroy was observed to feature "a lighter sound than on previous releases" and the album gave the opportunity for her to write all the lyrics. The album was released on 7 December 2009 and was later certified gold. A tour entitled "Le Cheshire Cat & Vous" to promote the record was held in 2010.
Leroy released a fourth studio album, Bretonne, on 6 December 2010. Cover versions of traditional Celtic songs such as "Mna na h-Eireann", "Tri Martolod", "La Jument de Michao", and contemporary songs such as Christophe Miossec's "Brest" were included on the album. Most of the songs related to Brittany, the singer's birthplace, four sung in Breton ("Tri Martolod", "Suite Sudarmoricaine", "Bro Gozh ma Zadou", "Karantez Vro"), one in Irish ("Mna na h-Eireann"), and the others in French and English. Leroy collaborated with Jon Kelly for the musical arrangements. The album topped the French album charts for 7 weeks and the Belgian album charts for 5 weeks. It was certified double diamond by the SNEP for sales exceeding one million copies.
The album was re-released in November 2011 as a Deluxe Edition which added 7 English language tracks, including "Amazing Grace", "Scarborough Fair" and two Mike Oldfield tracks, "Moonlight Shadow" and "To France". The American version of the album, retitled Nolwenn, was released on 8 January 2013 with a different track listing. The album peaked at number 10 on the Billboard's World Album chart. Leroy made her New York City debut at Drom. As part of the Bretonne Tour, Leroy played over 100 dates in France, Belgium, Switzerland and Germany.
Nolwenn Leroy released her fifth album on 26 November 2012, along with her leading single "Juste Pour Me Souvenir". The title reads 'O Daughters of the Water' but is phonetically identical to 'au fil de l'eau' ('with the current/flow'). Like Bretonne, it contains Celtic inspired music but with more ocean themed lyrics. The album includes two English-language tracks ("Homeland" and "Limitless"). The song "Homeland" contains the James Horner composed theme of the film Braveheart. "Ahes" is the only Breton-language song of the album. Leroy wrote and co-composed 9 songs, including the singles "Juste pour me souvenir", "Sixieme continent", "J'ai vole le lit de la mer" and "Ophelia". The album cover was created by Australian artist Vee Speers, inspired by her portrait series, Immortal.
Reviews of the album were strong, with some praising Leroy's vocal ability and Celtic music and lyrics, noting that her singing in English and Breton was brave and proved her to be an evolving artist, with strong sales to match. Two months after its release, the album was certified three times platinum by the SNEP.
In early 2014, she was nominated at the World Music Awards for the first time, in four categories: World's Best Album (Bretonne), World's Best Entertainer, World's Best Female Artist, and World's Best Live Act.
On 3 May 2014, Leroy performed the Breton anthem "Bro Gozh ma Zadou" at the Stade de France before 80,000 spectators, for the 2014 Coupe de France Final (aired on France 2) opposing two Breton clubs, the Stade Rennais to EA Guingamp.
Leroy's second live album, O Tour de L'Eau, was released on 1 December 2014.
On 11 June 2015, she was invited to talk about her career at Oxford University. In November 2015, Leroy announced that she would perform at Celtic Connections in Glasgow's City Halls on 30 January 2016, along with Karen Matheson.
Leroy's music was studied for its neurological impact in geriatric populations. Researchers found that Leroy's recordings might have a more beneficial effect than other music, noting that: "the music of Nolwenn Leroy was found to be significantly superior to other music tested". To describe the phenomenon they coined the term the Nolwenn Effect, saying: "the music of Nolwenn Leroy appears to have a different effect on brain-based modulation of gait and stance than other music tested to date".
Mozart and Dutch and French singers were tested; only Mozart and Leroy's music were specified. The U.S. study was completed in February 2008, but no substantial results appear to be published.
In 2011, Leroy appeared in two television commercials for the Nintendo 3DS and she became the face of Pantene for France and Belgium.
In 2006, she joined the Les Enfoires charity ensemble and she became one of the Abbe Pierre Foundation's patrons for housing people in need.
On the 27 November 2015, she participated together with Camelia Jordana and Yael Naim at the national memorial day for the victims of the November 2015 Paris attacks singing the song “Quand on n'a que l'amour” from Jacques Brel.
Since January 2008 she is dating Arnaud Clement, former French professional tennis player and the current captain of the France Davis Cup team.
* Belgium Ultratip2012: Die Wanderhure – Best Of (German TV movies)
2014: Song of the Sea (Original Motion Picture Soundtrack) and its French version Le Chant de la Mer
2012: Rise of the Guardians by Peter Ramsey, French voice of Tooth Fairy
2013: Lady O (evening show at the Futuroscope), the storyteller
2014: Song of the Sea by Tomm Moore, French voice of Bronagh
– denotes releases that did not chart.
Leroy owns a horse named El Aberkan. She showed her horse riding and jumping skills on unfamiliar horses a couple of times for French TV shows broadcast on France 2, including the 2011 Gala de l'Union des Artistes charity, alongside Alexis Gruss.
The main belt asteroid 353232 Nolwenn was named after Leroy.