O’Connor is born into a wealthy Irish Protestant family. Through his brother Roger O’Connor, the author of the Chronicles of Eri who shares his politics, he is an uncle to Roderic O’Connor, Francisco Burdett O’Connor, and Feargus O’Connor among others. His other two brothers, Daniel and Robert, are pro-British loyalists.
As a young man, O’Connor embraces the Republican movement early on as he is encouraged by the American Revolution overseas. After his oldest brother Daniel gets into debt, his brother Roger buys out his inheritance. The family’s political and financial conflicts are only deepened when their sister Anne commits suicide, after having been forbidden by the family from marrying a Catholic man she was in love with.
From 1790 to 1795 O’Connor is a Member of Parliament in the Irish House of Commons for Philipstown. The Irish House of Commons is part of the colonial parliament that sits in College Green, Dublin. He is also a member of the Kildare Street Club in Dublin.
In 1796, O’Connor joins the Society of United Irishmen and determines, on its platform, to contest what had been his uncle Lord Longueville’s Irish parliamentary seat in Antrim. In January 1797, to the “free electors” of the county he commends the “entire abolition of religious distinctions” and the “establishment of a National Government,” while protesting the “invasion” of the country by English and Scottish troops and the continuation of the continental war. Arrests, including his own in February for seditious libel, frustrate his attempts to canvass. With Lord Edward FitzGerald and others in the leadership in Dublin his thoughts turn to securing “fraternal” French support for a revolutionary insurrection.
While traveling to France in March 1798, O’Connor is arrested alongside Father James Coigly, a Catholic priest, and two other United Irishmen, Benjamin Binns (also of the London Corresponding Society), and John Allen. Coigly, who is found to be carrying an clear evidence of treason, an address from “The Secret Committee of England” to the French Directory, is hanged. O’Connor, able to call Charles James Fox, Francis Rawdon-Hastings, the Earl of Moria, Richard Brinsley Sheridan and other Whig luminaries to testify to his character, is acquitted but is immediately re-arrested and imprisoned at Fort George in Scotland along with his brother Roger.
O’Connor is released in 1802 under the condition of “banishment,” He travels to Paris, where he is regarded as the accredited representative of the United Irishmen by Napoleon who, in February 1804, appoints him General of Division in the French army. General Louis-Alexandre Berthier, Minister of War, directs that O’Connor is to join the expeditionary army intended for the invasion of Ireland at Brest. When the plan falls through, O’Connor retires from the army.
In 1807, although more than twice her age, O’Connor marries Alexandrine Louise Sophie de Caritat de Condorcet, known as Eliza, the daughter of the scholar the Marquis de Condorcet and Sophie de Condorcet. Following his marriage he borrows money from fellow exile William Putnam McCabe to acquire a country residence. His tardiness in repaying the debt to McCabe, whose own investments into cotton spinning in Rouen had failed, results in a lawsuit. Cathal O’Bryne suggests that the debt is behind O’Connor’s later suggestion to Richard Robert Madden that McCabe had been a double agent, a charge to which, Madden notes, the French government lends no credence.
O’Connor offers his services to Napoleon during the Hundred Days. After Napoleon’s defeat he is allowed to retire, becoming a naturalised French citizen in 1818. He supports the 1830 revolution which creates the July Monarchy, publishing a defence of events in the form of an open letter to General Gilbert du Motier, Marquis de Lafayette. After the revolution he becomes mayor of Le Bignon-Mirabeau. The rest of his life is spent composing literary works on political and social topics. He and his wife continue the efforts of her mother, who is herself an accomplished translator of Thomas Paine and Adam Smith, to publish her father’s works in twelve volumes between 1847 and 1849.
O’Connor’s wife give birth to five children, three sons and two daughters, almost all of whom predecease him. Only one son, Daniel, marries and has issue. Daniel marries Ernestine Duval du Fraville, a daughter of Laurent-Martin Duval, Baron Duval du Fraville, in 1843. She dies at Cannes in 1877.
O’Connor dies on April 25, 1852. His widow dies in 1859.
O’Connor’s descendants continue to serve as officers in the French army and still reside at Château Dubignon. Through his only surviving son, Daniel, he is a grandfather of two boys, Arthur O’Connor (1844–1909), who serves in the French army, and Fernand O’Connor (1847–1905), a Brigade General who serves in Africa and is made a Knight of the Legion of Honour. His grandson, Arthur, marries Marguerite de Ganay (1859–1940), a daughter of Emily and Etienne, Marquis de Ganay, in 1878. They have two daughters, Elisabeth O’Connor, the wife of Alexandre de La Taulotte, and Brigitte Emilie Fernande O’Connor (1880–1948), who in 1904 marries the Comte François de La Tour du Pin (1878–1914), who is killed ten years later at the First Battle of the Marne.