Charles O'Brien, 6th Viscount Clare

Bookplate with O'Brien's arms; note the marshal's batons and the collar of the Order of St Michael. Charles O'Brien, (17 March 16999 September 1761), titular 6th Viscount Clare and later titular 8th Earl of Thomond, was an Irish military officer in French service (he was made a Marshal of France), known to posterity as the Maréchal de Thomond.

Early life Charles O'Brien was the son of Charles O'Brien, 5th Viscount Clare and Charlotte Bulkeley, the sister of Anne Bulkeley, second wife of James FitzJames, 1st Duke of Berwick and Marshal of France. Murrough's death in 1741 caused the reversion to become effective, with the estates leaving O'Brien hands.

O'Brien was invested as a Knight, L'Ordre du Saint-Esprit of France on 2 February 1746 at the chapel of Versailles, Île-de-France, France. He held the office of Governor of Neuf-Brisach in Alsace, and was Commander-in-Chief of the province of Languedoc. In 1757 he was made a Marshal of France.

Personal life In 1755, O'Brien married Marie Genevieve Louise Gautier, daughter of François Gautier, marquis de Chiffreville. They had three children:

Charles O'Brien, 9th Earl of Thomond (1757–1774), who died unmarried.

Descendants Through his daughter Antoinette, he was a grandfather of Lucie-Virginie de Choiseul-Praslin (1794–1834), who married Charles Just de Beauvau, 4th Prince of Beauvau in 1815; and Charles-Félix de Choiseul-Praslin, 4th Duke of Praslin (1778–1841).