General responsibility for the government of Ireland was vested until 1922 in the Lord Lieutenant, who was assisted by the Chief Secretary for Ireland and the heads of governing boards of the Irish administrative departments. The Chief Secretary was constitutionally subordinate to the Lord Lieutenant and was originally the latter's nominee.
The relative political and administrative power of the two offices gradually altered, particularly after the Act of Union of 1801 which led to greater integration of the administrations of the two countries and to the residence of the Chief Secretary in London during the parliamentary session following the abolition of the Irish Parliament.
Both officers were members of the government of the United Kingdom and, on separate occasions, served in the Cabinet. The Lord Lieutenant represented the sovereign in Ireland holding formal court, presiding at meetings of the Irish Privy Council, and exercising the prerogative of mercy and considerable crown patronage. In addition to the viceregal powers granted in his commission, he possessed wide statutory powers, had direct executive authority over the Irish administrative departments (but not the courts of law), and general responsibility for the defence and the military establishments of Ireland. After 1801 all powers of appointment to regular army regiments and military command of such forces were transferred to the Commander-in-Chief in England.
The duties of the Chief Secretary were similar to those of the Secretary of State in Great Britain, with particular responsibility for parliamentary and legislative matters. He answered in Parliament for the policy and conduct of the Irish administration and was the normal channel of communication both between the Lord Lieutenant and the Irish departments and between the Irish administration and English departments. He also had considerable authority over the Irish departments generally as chief administrative officer to the Lord Lieutenant and immediately in the case of departments subordinate to the Chief Secretary's Office.
The Chief Secretary's Office in Dublin Castle was the central office of the Irish administration serving both the Lord Lieutenant and the Chief Secretary.
The office exercised close supervision over various Irish departments and conducted the bulk of correspondence with English departments. It was responsible for law and order, had oversight of the Royal Irish Constabulary and the Dublin Metropolitan Police, magistrates, prisoners and convicts, and transmitted the orders of the Irish Attorney-General (acting as Director of Public Prosecutions) to the police and crown solicitors. In 1919 the Chief Secretary became Minister of Health for Ireland and was assisted by an Irish Public Health Council.
The Chief Secretary's Office also maintained a separate establishment in London, known generally as the Irish Office, which handled Irish correspondence and dealt with certain parliamentary business.
Initially the office was headed by an Under-Secretary and also included a law adviser. After 1831 papers were frequently transmitted directly between the Chief Secretary's Office in Dublin and Whitehall departments, thereby reducing the work and the staff of the Irish Office in London. It was again enlarged in the late nineteenth century to meet the increase in parliamentary questions. The office also handled formal communications with the British government, particularly in matters of crown grants, warrants or commissions.
The Irish Office continued to function as a subsidiary branch of the Chief Secretary's Office until early in 1922 when most of the staff of the Dublin Office were transferred to London, along with selected records required for administrative purposes. The Irish Office was thereafter virtually responsible to two ministers: the Chief Secretary for arrangements for the transfer of functions to the new Irish authorities and the administration of reserved functions; and the Colonial Secretary for relations with the provisional government of Southern Ireland and questions relating to negotiations for the establishment of the Irish Free State. In October 1922 the office of Chief Secretary lapsed, but the Irish Office continued under the general direction of the Colonial Office. In December 1922 the office of Lord Lieutenant lapsed, the old Irish administration was wholly superseded and the Irish Office became the Irish Branch.
The various departments of the old administration were disbanded and their functions transferred to Irish Free State, Northern Ireland or United Kingdom departments.
Most of the records of the Irish administration and the Irish departments were transferred to the governments of the Irish Free State and of Northern Ireland.
In December 1922 responsibility for communications between the United Kingdom government and the governments of the Irish Free State and of Northern Ireland was assigned to the Colonial Office and the Home Office respectively. The Irish Office became the Irish Branch serving both departments. Sir John Anderson, who had been transferred to the Home Office as Permanent Under-Secretary in March 1922, continued to deal with Irish affairs and the Irish Branch was headed by Mark Sturgis, who remained as Assistant Under-Secretary for Irish Services until 1924. In April 1924 the branch was dissolved. The affairs of Northern Ireland became the responsibility of a new Northern Ireland Department of the Home Office, while relations with the Irish Free State were dealt with by the Dominions Division of the Colonial Office and, after 1925, by a department of the new Dominions Office.
The Northern Ireland Department (G Division) of the Home Office was formed; it also dealt with the Channel Islands and the Isle of Man. The Home Secretary assumed direct responsibility for relations with the government of Northern Ireland, for safeguarding the constitution of the province and for naturalisation, control of aliens and extradition; until 1926 he also exercised in Northern Ireland some powers assigned to the abortive Council of Ireland. The Home Office also took over from the Colonial Office in 1923 questions relating to pensions of the disbanded Royal Irish Constabulary, their administration and payment remaining the concern of the paymaster general.
In 1972 the Northern Ireland Department was taken over by the Secretary of State for Northern Ireland to form part of the new Northern Ireland Office.