William O'Shaughnessy (1673–1744) was an important figure in Irish history, recognized both as a hereditary chief and a military officer who became a French Major-General.
He is particularly notable for being the last hereditary chief of the O'Shaughnessy clan (The Ó Seachnasaigh) in the direct senior line to hold influence in their ancestral lands.
William O'Shaughnessy was a member of the Uí Seachnasaigh of Cenél Áeda na hEchtge in south County Galway, Ireland.
Birth and Ancestry: Born in Gort in 1673. His father was Roger O'Shaughnessy, The Ó Seachnasaigh (Chief of the Name), and his mother was Helen O'Brien, daughter of a son of the 4th Earl of Thomond.
Succession and Forfeiture: He inherited the title of The Ó Seachnasaigh upon his father's death in July 1690, following the Battle of the Boyne. However, due to the defeat of the Jacobite cause in the Williamite War in Ireland, his ancestral property was forfeited in 1697, and he was never able to return to his home.
Like many of the Irish nobility who left for Continental Europe after the Jacobite defeat (known as the "Wild Geese"), William O'Shaughnessy pursued a long and distinguished military career in the French army.
Early Service: He left for France in the spring of 1690 to serve in the Regiment of Daniel O'Brien. He began as a captain of a company composed of his own clan members and retainers.
Key Engagements: He fought for France in numerous conflicts, including the War of the League of Augsburg and the War of the Spanish Succession. Key actions he was present at include:
Siege of Montmelian (1691)
Battle of Marsaglia (1693)
Siege of Valenza (1696)
Kehl, Munderkingen, and the first and second battles of Blenheim (1703-1704)
Battle of Ramillies (1706)
Oudenaarde and Malplaquet (during the War of the Spanish Succession)
Promotions: His service led to significant promotions:
He was promoted to Major in 1706.
He was promoted to Lieutenant-Colonel in September 1706.
He became a Brigadier in April 1721.
He was made Maréchal de Camp (Major-General) in 1735.
Marriage: He married Maire Jacqueline Francoise de Gauville on February 15, 1729, at Aire-sur-la Lys. They had no children.
Death: He was appointed commander of the garrison at Gravelines in 1743 and died two months later on January 2, 1744, in France.
Succession of the Title: With his death without issue, the senior line of the O'Shaughnessy chiefs eventually died out around 1780 after a few subsequent successors from related branches. The O'Shaughnessy family's main branch was never able to recover their forfeited lands.