The Chief of Staff of the Defence Forces (COS) is charged with the executive management of the Irish Defence Forces, and is the most senior military officer of the Army, Naval Service and Air Corps branches. The Chief of Staff is appointed by the President of Ireland, who is the Supreme Commander of the Defence Forces, on the recommendation of the Minister for Defence subject to the approval of the Government of Ireland. The office of the Chief of Staff consists of his personal staff, a strategic planning office, a public relations section and the military judge.

Eoin O'Duffy was an Irish revolutionary, soldier, police commissioner and politician. O'Duffy was the leader of the Monaghan Brigade of the Irish Republican Army (IRA) and a prominent figure in the Ulster IRA during the Irish War of Independence. In this capacity, he became Chief of Staff of the IRA in 1922. He accepted the Anglo-Irish Treaty and as a general became Chief of Staff of the National Army in the Irish Civil War, on the pro-Treaty side.