Originally classically trained (violin and opera singing), she rose to fame after winning the second season of the French television music competition Star Academy in 2002.

In January 2015, she was ranked 17th on Le Journal du Dimanche's 50 Most Loved Celebrities in France, making her the top female singer on the list since December 2012.

At the age of thirteen she won "Les écoles du désert", 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.

[6] In July 1998, Leroy was awarded a scholarship by the Vichy Rotary Club to travel to Hamilton, Ohio, United States, as an exchange student.

[6] After watching the first season of Star Academy broadcast on TF1 in 2001, Leroy was impressed by Armande Altaï, a singing teacher and one of the show's judges.

In 2002, Nolwenn was selected for the second season of Star Academy, 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 Gérard Presgurvic.

As a contestant on the show, Leroy spent four months in a castle located in Dammarie-lès-Lys, and followed acting, dancing and singing classes.

Leroy's first album, Nolwenn, was released in March 2003 and was certified platinum by November[7] for sales exceeding 300,000 copies.

[8] In 2006, the album was certified two times platinum by the Syndicat national de l'édition phonographique (SNEP) for more than 600,000 copies sold.

Of the other single releases, "Mon Ange" was distributed digitally while "J'aimais tant l'aimer" and "Reste Encore" were promotional-only.

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.

Four of them were sung in Breton ("Tri Martolod", "Suite Sudarmoricaine", "Bro Gozh ma Zadoù", "Karantez Vro"), one in Irish ("Mná na h-Éireann"), and the rest in French and English.

[21] Leroy's fifth album, Ô filles de l'eau [fr], was released on 26 November 2012, preceded by the lead single "Juste pour me souvenir".

Leroy wrote and co-composed 9 songs, including the singles "Juste pour me souvenir", "Sixième continent", "J'ai volé le lit de la mer" and "Ophélia".

[22] The album cover was created by Australian artist Vee Speers, inspired by her portrait series, Immortal.

[32] In March 2015, she embarked on an acoustic tour in France, Belgium, Switzerland, Germany, New Caledonia and French Polynesia.

[33] 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.

The album features three songs in English: "Run It Down" and two poems by Edgar Allan Poe set to music ("A Dream" and "The Lake").

The album consisted of covers of contemporary folk songs, including Graeme Allwright's French adaptation of Suzanne by Leonard Cohen.

In July 2019, she was a special guest at Pink Martini's concert at Jazz à Juan festival.

[43] On 2 July 2021, Leroy released the lead single "Brésil, Finistère" from her eighth studio album La Cavale.

[46] In January 2022, it was announced that Nolwenn would join The Voice France as a surprise comeback stage coach for its eleventh season.

[59] In 2006, she joined the Les Enfoirés charity ensemble and she became one of the Abbé Pierre Foundation's patrons[60] for housing people in need.

[62] Since 2008, she has been in a relationship with Arnaud Clément, former French professional tennis player and captain of the France Davis Cup team.