John Joseph O'Kelly (known as Sceilg, an acronym of his name in Irish: Seán S. Ó Ceallaigh; 1872–26 March 1957) was an Irish politician, author and publisher. He was a former president of the Gaelic League and of Sinn Féin. He was born on Valentia Island off the County Kerry coast.
He joined Sinn Féin at its inaugural meeting on November 5, 1905. Following the 1916 Easter Rising, O'Kelly joined the Irish National League and became treasurer of the Irish National Aid and Volunteers' Dependants' Fund for the relief of prisoners and their families. In February 1917 he was arrested and deported to England where he was interned without trial for several months. On his release O'Kelly was elected to the Provisional Committee of the newly merged Irish National League and Sinn Féin, thereafter called Sinn Féin. He was appointed editor of the influential "Catholic Bulletin".
In the United Kingdom general election, 1918 he was elected as a Sinn Féin MP for Louth by 255 votes in what was the closest contest in Ireland in that election. The closeness of the contest was due to the strong AOH organisation in the county that campaigned for outgoing North Galway MP Richard Hazleton of the Irish Parliamentary Party.
O'Kelly took his seat in Dáil Éireann as a Sinn Féin Teachta Dála and was elected Leas-Cheann Comhairle (vice) Ceann Comhairle in 1919-21. He was Secretary for Education in the Government of the 2nd Dáil. From 1919 to 1923, he was President of the Gaelic League. He opposed the Anglo-Irish Treaty that was ratified by the Dáil in January 1922, and refused to accept the legitimacy of the Irish Free State established in December 1922. He and others maintained that the Irish Republic continued to exist and that the rump of the Second Dáil, composed of those anti-Treaty TDs who had refused to take their seats in what became the Free State parliament, was the only legitimate government for the whole of Ireland. He was elected to the Third Dáil but abstained from taking his seat. After the resignation of Éamon de Valera as president of Sinn Féin in 1926, O'Kelly was elected in his place and remained in this position until 1931.
He was a prolific author on Irish language and history topics, editing Banba, The Catholic Bulletin and An Camán. He was intensely religious and a conservative Roman Catholic. Many of his speeches and writings contained anti-Semitic and anti-Masonic content. In 1916, members of Ireland's Jewish community protested after the Bulletin published a series of articles by Fr. T.H. Burbage accusing the Jewish community of carrying out ritual murders; O'Kelly refused to apologise for the articles. O'Kelly opposed members of the IRA fighting against Franco in the Spanish Civil War. In 1938, he was one of seven remaining abstentionist Second Dáil TDs who transferred the "authority" of what they believed was the "authority" of the Government of the Irish Republic to the IRA Army Council (see Irish republican legitimatism).
In 1938, he visited Germany, later publishing his impressions in the Irish Independent.
O'Kelly died in Our Lady's Hospice, Harold's Cross, on 26 March 1957, and was buried in Glasnevin Cemetery on March 28.