Liam Deasy, Irish Republican Army (IRA) officer who fights in the Irish War of Independence and the Irish Civil War, is born in Kilmacsimon, Bandon, County Cork on May 6, 1896. In the latter conflict, he is second-in-command of the anti-Treaty forces for a period in late 1922 and early 1923. Before the anti-Treaty and pro-Treaty split, he is considered closely associated with Michael Collins.

Deasy is the third among six sons of William Deasy, seaman, and Mary Deasy (née Murray). He is educated locally at Ballinadee before leaving school at the age of thirteen to work in nearby Bandon.

During the Irish War of Independence (1919–21), Deasy is adjutant of the IRA’s 3rd Cork Brigade (West Cork). He serves under Tom Barry in one of the unit’s best known actions, the Crossbarry ambush in March 1921. His younger brother, Pat, dies in action at the Kilmichael ambush in November 1920, an engagement at which Deasy is not present. He also takes part in the Tooreen ambush.

Deasy opposes the Anglo-Irish Treaty. In the months that follow he tries to persuade Collins to renegotiate aspects of the treaty, especially to remove an oath to the British king from the constitution of the new Irish Free State. When fighting breaks out in Dublin in June 1922 between pro and anti-Treaty forces, he sides with the Anti-Treaty IRA in the ensuing Irish Civil War. However, he is reluctant to fight his former comrades and voices the opinion that the fighting should have ended with the Free State seizure of the Four Courts.

In late July 1922, Deasy commands 1,500 anti-Treaty fighters who hold a line around Kilmallock south of Limerick city against about 2,000 Free State troops under Eoin O’Duffy. His men are the most experienced IRA fighters of the 1919-21 war and hold their position until August 8, when they are outflanked by seaborne landings on the southern coast. His men then disperse. He goes on the run in the southeast of the country.

In August 1922, Deasy is in command of a band of republican guerrillas in West Cork when they hear that Collins is in the area. Deasy has his men prepare an ambush for Collins’ convoy at Béal na Bláth, should it return by the same route it had taken earlier.

Deasy and most of his men do not take part in the ambush as they had retired to a nearby pub, assuming that they had missed Collins. However, Collins arrives as the last of Deasy’s men are clearing the mine and barricade that had been erected on the road at Béal na Bláth. Collins is killed in the ensuing firefight. Deasy later writes in his memoirs that he profoundly regrets the death of his former commander.

In January 1923, by which time Deasy has become Deputy Chief of Staff of the IRA, he is captured by Free State forces near Clonmel, County Tipperary, and sentenced to death. He is aware that the newly formed government plans on wholesale executions and knows that the IRA will retaliate with reprisals. He decides that it is now time to end the war. He signs a document (written by his captors) ordering the men under his command to surrender themselves and their arms to the government. He is spared execution. On the day that his order is published, Free State authorities demand that the prisoners in a jail in Limerick sign a statement agreeing to unconditional surrender, threatening wholescale executions to those who refused. Some republicans denounce Deasy as a traitor and a coward for this action, but he argues in his book, Brother against Brother, that he was opposed to continuing the civil war anyway and would have called on republicans to surrender whether or not he had been captured.

Deasy takes no further part in politics following the end of the Irish Civil War. In 1924, he sets up a business making weatherproof textiles. On November 24, 1927, he marries Margaret Mary O’Donoghue. They have three daughters together.

During The Emergency, Deasy serves in the Irish Army from 1940 to 1945, reaching the rank of commandant. He later writes two memoirs about his experiences during the revolutionary period: Toward Ireland Free and Brother against Brother, the latter being published after his death.

Deasy dies at St. Anne’s Hospital, Northbrook Road, Dublin, on August 20, 1974. He is buried in Bohernabreena Cemetery in Dublin.