Percy Wyndham-O'Brien, 1st Earl of Thomond

Percy Wyndham-O'Brien, 1st Earl of Thomond (c. 1713–1774) was a British Member of Parliament and an Irish peer.

He was the younger of the two sons of Tory statesman Sir William Wyndham, 3rd Baronet (c.1688-1740) of Orchard Wyndham, Somerset, Secretary at War in 1712, Chancellor of the Exchequer in 1713 and Tory leader in the House of Commons during the reign of King George I (1714-1727) and during the early years of King George II (1727-1760). His mother was Catherine Seymour, daughter of Charles Seymour, 6th Duke of Somerset (1662-1748), KG, and sister of Algernon Seymour, 7th Duke of Somerset (1684-1750), created in 1749 Earl of Egremont and Baron Cockermouth, with special remainder to his nephew Charles Wyndham (1710-1763), Percy's elder brother, who duly became 2nd Earl of Egremont in 1750.

When Percy was 28 years old in 1741, Henry O'Brien, 8th Earl of Thomond died without issue and in his will left all his Irish estates to his nephew Percy Wyndham, the younger son of his wife's sister. In compliance with the terms of the bequest, Percy took the additional surname name of O'Brien. On 11 December 1756 he was created Earl of Thomond and Baron Ibracken (the second creation).

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