It replaced both the Irish Republic and Southern Ireland . The Irish Free State effectively replaced the self-proclaimed Irish Republic ( itself established on 21 January 1919 ) . Similarly , the new government of the Irish Free State replaced both the Provisional Government of Southern Ireland and the Government of the Irish Republic although W. T. Cosgrave , the first President of the Executive Council of the Irish Free State had , in any event , led both governments since August 1922 .