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For other people called John O'Mahony, see John O'Mahony (disambiguation).

John O'Mahony (1816–1877) was the founding member of the Fenian Brotherhood in America, sister organisation to the Irish Republican Brotherhood.

Early life[]

He was born in 1816 in Kilbeheny, County Limerick, Ireland. His father and uncle had been members of the United Irishmen, and had taken part in the Irish Rebellion of 1798. He ignored the ban by the Roman Catholic Church on its adherents attending Trinity College, Dublin, where he studied Sanskrit, Hebrew and Irish.


He joined Daniel O'Connell's movement for the Repeal of the Union, but quickly became dissatisfied with the lack of progress.

Rebellion in 1848[]

He joined the Young Irelander movement and took part in their failed rebellion in 1848.


He left Ireland for France, where he lived in great poverty, and moved to the United States in 1852. It has been said that the Fenian Society originated in America and was transplanted to Ireland; but, as a matter of fact the plans for both the Irish and American organizations were drawn in Paris by a small group of the Irish revolutionary exiles in 1848.

Fenian Brotherhood[]

File:Fenian Plot Glasnevin, Dublin..jpg

Grave of John O'Mahony in the Fenian Plot, Glasnevin, Dublin

In 1854–58, he organized the American wing of the IRB, initially known as the Fenian Brotherhood. Its principal object was to supply money and arms to the Irish branch. The Civil War in the United States gave the Fenians a great opportunity to obtain military training. A large part of the Irish soldiers engaged on both sides in the struggle were Fenians. Because of his popularity among Irish-Americans he was soon-after made a colonel in the mainly Irish 69th Regiment of the Union Army, which fought in the American Civil War. He helped organise the first of the Fenian Raids into the then British colony of Canada in 1866 and the Fenian Rising in Ireland in 1867.


In his later years he had a hard struggle to secure the bare means for subsistence. He died in New York in 1877 and was interred in Glasnevin Cemetery in Dublin.


  • The History of Ireland by Geoffrey Keating, D. D., Translated from the Gaelic and Copiously Annotated (1857)


  • Alfred Webb, A Compendium of Irish Biography (Dublin, 1888)

See also[]


ca:John O'Mahony ga:Seán Ó Mathúna tr:John O'Mahony