Society formed in 1791 by Wolfe Tone to campaign for parliamentary reform in Ireland. It later became a secret revolutionary group.
Inspired by the republican ideals of the French Revolution, the United Irishmen was initially a debating society, calling for reforms such as the right of Catholics to vote in Irish elections, but after an attempt to suppress it in 1793, the organization became secret, looking to France for military aid. An attempted insurrection in 1798 was quickly defeated and the leaders captured.
The idea of a brotherhood of Irishmen of all religions dedicated to political reform originated with William Drennan (1754–1820) a Belfast physician and poet. The first United Irish Society was started in Belfast in 1791 by Wolfe Tone, Thomas Russell, and others. Similar societies soon appeared in Dublin and parts of Ulster. These societies campaigned legally for parliamentary reform and Catholic emancipation. However, the United Irishmen supported the ideas of the French Revolution and began from 1795, after their reform campaign had failed, to reorganize as an underground revolutionary movement. They established an alliance with the Catholic Defenders, and sought French military aid for a rebellion intended to overthrow British rule in Ireland. A large French fleet, with Wolfe Tone on board, was only prevented from landing by storms in December 1796. Government advisors, particularly the lord chancellor John Fitzgibbon, 1st Earl of Clare (1749–1802), advocated a campaign of severe repression against the United Irishmen. Many informers were recruited. This resulted in arms seizures and arrests of leaders which diminished the chances of a successful insurrection. Though badly damaged, the United Irish movement survived the Rebellion of 1798. Some new leaders, such as Robert Emmet and Thomas Russell, tried to organize a new rebellion in 1803. However they attracted little support and their uprisings were easily crushed.