James Stephens formally establishes the Irish Republican Brotherhood (IRB) in Peter Lanigan’s timber yard, Lombard Street, Dublin, on Saint Patrick’s Day, March 17, 1858. It is originally named the Irish Revolutionary Brotherhood, but soon comes to be known as the Irish Republican Brotherhood. At the same time, John O’Mahoney is founding the American branch of the revolutionary group. O’Mahoney gives the organization the better-known name Fenians, in honor of the Fianna, the soldiers led by Fionn mac Cumhaill, the heroic warrior of Irish legend.

The IRB is a small, secret, revolutionary body whose sole object is to “establish and maintain a free and independent Republican Government in Ireland.” Stephens is a Young Irelander and is a lieutenant to William Smith O’Brien at the Battle of Widow McCormack’s Cabbage Patch in Ballingary, County Tipperary, in August 1848. He is wounded three times and is smuggled onto a ship to England and then to France, where he spends the next eight years. Upon his return to Dublin in 1856, he determines to organise a revolutionary movement and that leads to the founding of the IRB.

The IRB becomes known as the Fenian movement in the 1850s and 1860s and is committed to the use of force to establish an independent Irish republic. After organising an abortive rising in March 1867, it suffers deep internal divisions over its leadership and strategy in both the United States and Ireland—whether it is best to strike at England, in Ireland or in Canada. The issue is resolved after a series of failed interventions in Canada in 1866, 1867 and 1871, and after bombings in England that do not lead Ireland closer to independence. The IRB is unable to exploit the weaknesses and divisions in the constitutional movement following Charles Stewart Parnell’s divorce scandal (1890–91).

The IRB is eventually rejuvenated in Ireland about 1907, led by Bulmer Hobson and Tom Clarke, thus preparing the way for all that follows.The governing body is the Supreme Council. Before 1916 this consists of eleven members, and after the 1917 reorganisation it contains fifteen members. When not in session, all powers of the Supreme Council, except for declaring war, devolve onto an executive of three: the president, secretary and treasurer.

The constitution provides for the establishment of a military council, subordinate to the Supreme Council. The seven signatories of the 1916 Proclamation of the Irish Republic constitute the entire military council at the time. The constitution is dedicated to the use of force against England at any favourable opportunity, but this is to be a democratic decision: “The IRB shall await the decision of the Irish Nation as expressed by a majority of the Irish people as to the fit hour of inaugurating a war against England and shall, pending such an emergency, lend its support to every movement calculated to advance the cause of Irish independence, consistent with the preservation of its own integrity,” a clause adopted in 1873 in response to the controversies arising from the 1867 Fenian Rising.

The IRB plans the 1916 Easter Rising but the Irish Volunteers and the Irish Citizen Army make it possible. The establishment of the Irish Volunteers gives the IRB the great opportunity to train and equip its members as a military body for the purpose of securing independence for Ireland by force of arms and securing the cooperation of all Irish military bodies in the accomplishment of its objectives. Numerically the IRB probably never exceeds 2,000 members, but they are all extremely loyal and well trained, and there is very tight security. The executions of 1916 just about wipe out the Supreme Council, and after the prisoners are released, the IRB has to reconstitute itself.

Following the Easter Rising some republicans—notably Éamon de Valera and Cathal Brugha—leave the organization, which they view as no longer necessary, since the Irish Volunteers now perform its function. The IRB, during the Irish War of Independence (1919-21), is under the control of Michael Collins, who is secretary, and subsequently president, of the Supreme Council. Volunteers such as Séumas Robinson say afterwards that the IRB by then is “moribund where not already dead,” but there is evidence that it is an important force during the war.

When the Anglo-Irish Treaty is signed on December 6, 1921, it is debated by the Supreme Council, which votes to accept it by eleven votes to four. Those on the Supreme Council who oppose the Treaty include former leader Harry Boland, Austin Stack and Liam Lynch. Anti-Treaty republicans like Ernie O’Malley, who fought during the Irish Civil War against the Treaty, sees the IRB as being used to undermine the Irish Republic. The IRB becomes quiescent during the Irish Civil War, which ends in May 1923, but it emerges again later that year as a faction within the National Army that supports Minister for Defence Richard Mulcahy against the “Old IRA,” which fought against the recruitment of ex-British Army personnel and the demobilization of old IRA men. This comes to a head with the Irish Army Mutiny of 1924, in the wake of which Mulcahy resigns and other IRB members of the army are dismissed by acting President of the Executive Council Kevin O’Higgins. The IRB subsequently dissolves itself, although it is not known whether a formal decision is taken, or it simply ceases to function.