Ciarán Brennan, born Ciarán Ó Braonáin on March 4, 1954, is an Irish musician and composer, best known as a member of the band Clannad. He hails from Gweedore, County Donegal, Ireland, a region known for its rich musical heritage and Irish-speaking community. Ciarán is the son of Leo Brennan and Máire 'Baba' Duggan and is part of a musically talented family that includes his siblings Moya (Máire), Pól, and Enya (Eithne), among others.

Ciarán Brennan's contributions to Clannad have been significant, as he played various instruments including the double bass, electric bass, guitar, synthesizer, and piano, while also providing vocals. Clannad, formed in 1970 by the Brennan siblings and their uncles Noel and Pádraig Duggan, gained international recognition with their unique blend of traditional Irish music, folk, rock, and new age elements. The band is credited with bringing Irish music and the Irish language to a global audience, achieving numerous awards and accolades, including a Grammy Award.

Throughout his career with Clannad, Ciarán Brennan has been instrumental in the band's evolution, contributing to their innovative sound that incorporates vocal harmonies, electronic keyboards, and elements of Celtic and Gregorian chant. Clannad's music has been influential in defining the Celtic genre, and they have recorded in multiple languages, achieving significant success both in Ireland and internationally.