In 1926 when de Valera left Sinn Féin to found his own republican party, Fianna Fáil, Ó Ceallaigh followed him, becoming one of the party's founding members. In 1932, when de Valera, was appointed President of the Executive Council (prime minister) of the Irish Free State he made Ó Ceallaigh Minister for Local Government. Ó Ceallaigh often tried to publicly humiliate the Governor-General of the Irish Free State, James McNeill. Stunts such as withdrawing the Irish Army's band from playing at diplomatic functions which the Governor-General attended, or in one notorious case the sight of O'Kelly and Defence Minister Frank Aiken storming out of a diplomatic function at the French Legation when McNeill, the guest of honour, arrived, damaged Ó Ceallaigh's reputation and image, particularly when the campaign backfired.