Michael Corcoran was born in Carrowkeel, near Ballymote, Co Sligo. He was the only child of Thomas Corcoran, an officer in the British army, and Mary McDonagh. He claimed descent from Patrick Sarsfield on his mother’s side. Michael attended school in Ballymote, until the age of eighteen.
He joined the Revenue Police at age nineteen and was stationed in Donegal. While still a member of the police force Corcoran became a member of the Ribbon Society, a secret organisation dedicated to the rights of tenants. He kept up his double life for almost two years before leaving the police. There is some inconclusive evidence that his activities as a Ribbonman were uncovered, hence his sudden departure for the United States in August of 1849.
After arriving in the United States he worked a number of jobs including that of manager at the Hibernian Hall in New York City. There he met and married Elizabeth Heaney the niece of John Heaney who operated the Hibernian Hall tavern. He was also active in Tammany Hall politics.
He enlisted as a private in the 69th New York Militia in 1859, served in every rank and within three years was promoted to captain. From there he went on to achieve the rank of Colonel.
In 1860 he was ordered to parade the regiment in honour of the visiting 19-year-old Prince of Wales, the son of the English queen who had presided over An Gorta Mór that reduced the population of Ireland by half. Corcoran issued a statement that he “could not in good conscience order out a regiment composed of Irish-born citizens to parade in honour of a sovereign under whose reign Ireland was made a desert and her sons forced into exile.”
His refusal infuriated the Anglophiles who demanded his court martial. Because anti-Catholic and anti-Irish hatred and bigotry were still very much alive in the U.S., Corcoran was stripped of his command and placed under arrest. However, during the court martial proceedings, Fort Sumter was fired upon signaling the beginning of the civil war. As a consequence all court martial proceedings were dropped. The war made him an important asset to the U.S. Army because of his ability to recruit Irish volunteers.
In the war, Corcoran initially led the 69th New York State Militia in the First Battle of Bull Run in 1861. During the defeat and retreat of the Union army he was taken prisoner. Corcoran was one the Union officers chosen by lot to become a Confederate hostage in the Enchantress Affair. Together with the other hostages he was threatened with execution if the United States government executed the crew of the Confederate Navy ship Enchantress, a merchant schooner pirated and put in use by the Confederate government. Both sides backed off the threat of executions.
Corcoran was one of the founders of the Fenian Brotherhood in America. While in jail, Corcoran wrote, “One half of my heart is Erin’s, and the other half is America’s. God bless America, and ever preserve her the asylum of all the oppressed of the earth, is the sincere prayer of my heart.”
Corcoran was exchanged for two Confederate diplomats in August of 1862. Upon his release, he was commissioned a Brigadier General and was invited to have dinner with President Lincoln. Lincoln asked him to recruit what would be a second Irish Brigade for the army of the Potomac. With the help of his comrades of the 69th he raised the Irish Legion of four regiments that ringed Washington in defensive positions.
During the last brutal year of the war Corcoran’s Legion fought alongside the Irish Brigade that had been raised by the former Young Irelander, Thomas Francis Meagher.
General Corcoran was killed when he fell off his horse and was trampled on while riding with General Meagher.
Corcoran was the highest ranking American general (a division commander) to be simultaneously a member of the Fenian Brotherhood.