At the age of 14, Chloë appeared on stage as one of the original members of Celtic Woman at The Helix in Dublin. This performance was first broadcast on PBS in 2005 in the United States, and within weeks the group's eponymous debut album Celtic Woman, reached No. 1 on Billboard's World Music chart. The album held the top position on the Billboard World Music chart for 81 weeks in total. The release of the second album, Celtic Woman: A Christmas Celebration, in 2006 knocked their first album to the No. 2 spot on the World Music chart. In preparation for their third studio album, Celtic Woman performed at Slane Castle in County Meath, Ireland, with this show airing on PBS in December of 2006. Their next studio album, titled Celtic Woman: A New Journey, was released in January 2007. This album immediately hit the Billboard 200 at No. 4 and the Billboard World Music chart at No. 1, moving their previous two releases down a notch and securing the top three positions on that chart for the group. In 2007 Celtic Woman won the European Border Breakers Award (EBBA), who recognize the success of ten emerging artists or groups who reached audiences outside their own countries with their first internationally released album.
To date Chloë has featured on a total of 14 of Celtic Woman’s albums. She has recorded in English, Irish, Latin, Japanese, Italian and German on their various albums which have sold more than eight million copies of its releases worldwide, all of which have debuted at #1 on Billboard's World Music chart. During Chloë's tenure with Celtic Woman, the group sold out concerts in prestigious venues throughout the globe including Carnegie Hall, Red Rocks, Colorado, Radio City Music Hall and several O2 Arena’s in Europe, performing for nearly three million fans. In 2009 she collaborated with renowned Italian tenor, Alessandro Rinella and Warner Chapel Music producer Leo Z on the song L'assenza. Chloë has also had the pleasure of collaborating with many other artists during her time with Celtic Woman, including Chris De Burgh, Anne Murray and Selim Kagee. Throughout the years Chloë performed with Celtic Woman on US Television shows such as Dancing with the Stars, Regis and Kelly, The Today Show, Good Morning America and the hugely successful show The Bold and the Beautiful. Chloë has also had the incredible honor of performing for the three former US presidents before she reached the age of 20. In 2012 she was named Best Vocalist at the Irish Music Awards.
In 2013, Chloë announced her plans to embark on a solo career.