The mainly ceremonial office of Governor of Northern Ireland is abolished on July 18, 1973 under Section 32 of the Northern Ireland Constitution Act 1973. The Secretary of State for Northern Ireland, a cabinet office created in 1972, takes over the functions of the Governor on December 20, 1973 under Letters Patent.
The office of the Governor of Northern Ireland is established on 9 December 9, 1922 under Letters Patent to “do and execute in due manner as respects Northern Ireland all things which by virtue of the  Act and our said Letters Patent of 27 April 1921 or otherwise belonged to the office of Lord Lieutenant at the time of the passing of the Irish Free State Constitution Act 1922.”
The 1922 “Instructions” sent alongside the letters patent establishing the office require the Governor of Northern Ireland to get the monarch’s permission to leave Northern Ireland, and empowers the Governor in such cases to issue letters patent under the Great Seal of Northern Ireland appointing a “Deputy or Deputies, Justice or Justices” during his absence. This emulates the practice of appointing Lords Justices of Ireland when the Lord Lieutenant is absent from Ireland. Each new Governor upon taking office selects a slate of eligible deputies from among the Privy Council of Northern Ireland, and at each of his subsequent absences a subset of these are sworn in for its duration. Many are Lord Chief Justice or Lord Justice of Appeal, including Denis Henry, William Moore, James Andrews, Anthony Babington, John MacDermott, Baron MacDermott, and Samuel Clarke Porter. Others are Senators and/or county lieutenants, including Robert Sharman-Crawford, Robert David Perceval-Maxwell, Henry Armstrong, Sir Thomas Dixon, 2nd Baronet, Maurice McCausland, and Francis Needham, 4th Earl of Kilmorey.
The Governor has possession of the Great Seal of Northern Ireland and is the successor to the Lord Lieutenant of Ireland in Northern Ireland, itself established on May 3, 1921. The official residence of the Governor of Northern Ireland is Hillsborough Castle in County Down. Following refurbishment of the Castle, James Hamilton, 3rd Duke of Abercorn, takes up residence in 1925. It remained the official residence until the abolition of the office of governor in 1973. Henceforth it has been the official residence of the Secretary of State for Northern Ireland.