Brugha is born Charles William St. John Burgess of mixed Roman Catholic and Protestant parentage in Dublin on July 18, 1874. He attends Colmkille Schools until 1888 when he is admitted to Belvedere College. He intends to study medicine but this does not come to fruition after his father’s business fails in 1890. He is seen as an austere figure, not very different from Éamon de Valera, and is known not to smoke cigarettes, swear or drink alcohol.
In 1899, Brugha joins the Gaelic League, and he subsequently changes his name from Charles Burgess to Cathal Brugha. He meets his future wife, Caitlín Kingston, at an Irish class in Birr, County Offaly, and they marry in 1912. The marriage produces six children. He becomes actively involved in the Irish Republican Brotherhood (IRB) and in 1913 he becomes a lieutenant in the Irish Volunteers. He leads a group of twenty Volunteers to receive the arms smuggled into Ireland in the Howth gun-running of 1914.
Brugha is second-in-command at the South Dublin Union under Commandant Éamonn Ceannt in the Easter Rising of 1916. On the Thursday of Easter Week, being badly wounded, he is unable to leave when the retreat is ordered. Brugha, weak from loss of blood, continues to fire upon the enemy and is found by Eamonn Ceannt singing “God Save Ireland” with his pistol still in his hands. He recovers over the next year, but is left with a permanent limp.
Brugha proposes a Republican constitution at the 1917 Sinn Féin convention, which is unanimously accepted. In October 1917, he becomes Chief of Staff of the Irish Republican Army and holds that post until March 1919.
Brugha is elected as a Sinn Féin MP for the County Waterford constituency at the 1918 Irish general election. In January 1919, Sinn Féin MPs refuse to recognise the Parliament of the United Kingdom and instead assemble at the Mansion House in Dublin as a revolutionary parliament called Dáil Éireann. Owing to the absence of Éamon de Valera and Arthur Griffith, he presides over the first meeting of Dáil Éireann on January 21, 1919.
Brugha is elected Ceann Comhairle of Dáil Éireann at its first meeting on January 21, 1919, and he reads out the Declaration of Independence in Irish, which ratifies “the establishment of the Irish Republic.” On the following day he is appointed president of the ministry pro tempore. He retains this position until April 1, 1919, when Éamon de Valera takes his place.
Brugha has differences with Michael Collins, who, although nominally only the Irish Republican Army‘s (IRA) Director of Intelligence, has far more influence in the organisation as a result of his position as a high-ranking member of the IRB, an organisation that Brugha sees as undermining the power of the Dáil and especially the Ministry for Defence. He opposes the oath of allegiance required for membership of the IRB. In 1919, his proposition that all Volunteers should swear allegiance to the Irish Republic and the Dáil is adopted.
At a top-level IRA meeting in August 1920, Brugha argues against ambushes of Crown forces unless there is first a call to surrender, but it is dismissed as unrealistic by the brigade commanders present. He also has the idea of moving the front line of the war to England, but is opposed by Collins.
On January 7, 1922, Brugha votes against the Anglo-Irish Treaty. During the Treaty debates, he points out that Collins has only a middling rank in the Department for Defence, which supervises the IRA, even though Griffith hails him as “the man who had won the war.” It is argued that, by turning the issue into a vote on Collins’ popularity, Brugha swings the majority against his own side. Frank O’Connor, in his biography of Collins, states that two delegates who had intended to vote against the Treaty changed sides in sympathy with Collins. Brugha leaves the Dáil and is replaced as Minister for Defence by Richard Mulcahy.
In the months between the Treaty debates and the outbreak of Irish Civil War, Brugha attempts to dissuade his fellow anti-treaty army leaders, including Rory O’Connor, Liam Mellows and Joe McKelvey, from taking up arms against the Free State. When the IRA occupies the Four Courts, he and Oscar Traynor call on them to abandon their position. When they refuse, Traynor orders the occupation of the area around O’Connell Street in the hope of easing the pressure on the Four Courts and of forcing the Free State to negotiate.
On June 28, 1922, Brugha is appointed commandant of the forces in O’Connell Street. The outbreak of the Irish Civil War ensues in the first week of July when Free State forces commence shelling of the anti-treaty positions.
Most of the anti-Treaty fighters under Traynor escape from O’Connell Street when the buildings they are holding catch fire, leaving Brugha in command of a small rearguard. On July 5, he orders his men to surrender, but refuses to do so himself. He then approaches the Free State troops, brandishing a revolver. He sustains a bullet wound to the leg which “severed a major artery causing him to bleed to death.” He dies on July 7, 1922, eleven days before his 48th birthday. He had been re-elected as an anti-Treaty TD at the 1922 Irish general election but dies before the Dáil assembles. He is buried in Glasnevin Cemetery in Dublin.