The family moved to Wales where, exposed to Breton and Welsh folk music, Katell began singing, mainly in choirs and eisteddfodau.
She has cited the film, The Song Remains the Same as influential; she watched it in the same year she began busking in Cardiff, which led to travels around the United Kingdom and Ireland playing at ad hoc gigs and festivals.
Her first release was a seven-inch single called "Hestia" on SOL, an independent label co-owned by musicians Bob Mould and Nicholas Hill.
A six-page, high-profile interview with Darcy Frey was published on 2 July 2006 in The New York Times Magazine and this sparked new interest in Keineg's music in the United States.
During the rest of 2006 and into 2007, Keineg played several sold out concerts in New York in the wake of the article, including a month-long Friday night residency at The Living Room in February 2007.
Mid-2007 was spent playing European classical music festivals with concert pianist Katia Labeque's experimental band, B For Bang, whose first album was released in January 2008 and included a version of The Beatles "I Want You (She's So Heavy)" sung by Keineg.
She released a 4-song EP in January 2009 that includes the re-recorded "On Yer Way", a Welsh language cover of the Super Furry Animals song "Y Gwyneb Iau" and "Trouble", an outtake from "Jet" re-mixed by Scott.
She toured in the UK and Ireland following the album's release, opening for singer-songwriter Krystle Warren and playing The Green Man festival.