Seán T. Ó Ceallaigh was born in inner-city Dublin on 25 August, 1882. He joined the National Library of Ireland in 1898 until 1902 as a junior assistant to T.W. Lyster. In 1902 he joined the Gaelic League and became the general secretary in 1915. Ó Ceallaigh worked for Arthur Griffith and joined Sinn Féin as one of its founders in 1905 and became a joint honorary secretary of the movement. In 1906 he was also elected to the Dublin Corporation. Ó Ceallaigh was one of the establishing members of the Irish Volunteers in 1913 and in 1915 went to New York City to inform Clan Na Gael of the plans for a rising in Dublin by the IRB. Padraic Pearse appointed him to be his Staff Captain for the insurrection. Ó Ceallaigh was at the heart of the organisation of the Rising and during the event he was in and out of the GPO. It was also during the Rising that he met Mary Kate (Kit) Ryan and the two married in 1918. Following the Rising, Ó Ceallaigh was imprisoned in England and later returned to Ireland where he was elected as a Sinn Féin MP for Dublin College Green in the 1918 General Election. Along with other Sinn Féin members, he refused to take his seat and they instead established Dáil Éireann and Ó Ceallaigh served as Ceann Comhairle. Ó Ceallaigh also published the democratic programme which he edited. He was a close associate of Éamon de Valera and the two opposed the 1921 Anglo-Irish Treaty. During the Civil War, Ó Ceallaigh was in jail until 1923, after which he spent two years as a Sinn Féin envoy to the United States. When de Valera established Fianna Fáil in 1926, Ó Ceallaigh was appointed vice-president of the party and in 1927 he became editor of ‘The Nation’. Later in 1937 with the enactment of a new constitution, Ó Ceallaigh remained the second in command in the government with the new title of Tánaiste. He became the Minister for Finance in 1939 and secured the passing of ‘The Central Bank Act’ in 1942. Ó Ceallaigh ecame the 2nd president of Ireland in 1945 and was the first president of Ireland to visit the United States of America in 1959 as the guest of president Dwight Eisenhower. He died on 23 November 1966 and is buried in Glasnevin Cemetery in Dublin.