Born in Dublin and educated in Nice, Clongowes Wood and Trinity College Dublin, he was founder and editor of the magazine Hibernia, a review of literature and art. He married Josephine Cranny in 1884 and was called to the Bar the following year but never practiced. He developed a career in literature, art criticism and culture, serving as Director of the National Museum (1907–16), Vice-President of the Royal Irish Academy (1908–9, 1911–14) and President of the Royal Society of Antiquaries of Ireland as well as a multiplicity of other cultural, language and artistic organisations and institutions. He was politicised by the execution of one of his sons, Joseph Mary, an organiser of the 1916 Rising, and was returned as an abstentionist independent MP for North Roscommon in the 1917 by-election. He served as Minister for Foreign Affairs in the First Dáil Éireann (January 1919–August 1921), accompanying Eamon de Valera to London for the negotiations with Lloyd George in July 1921, and as Minister for Fine Arts (August 1921–January 1922). He opposed the Treaty, refused to take the seat he held for Roscommon, and continued to support Sinn Féin after the split with Fianna Fáil.