Pinckney, Thomas, 1750–1828, American political leader and diplomat, b. Charleston, S.C.; brother of C. C. Pinckney and cousin of Charles Pinckney. At the outbreak of the American Revolution he joined the militia; he saw action in Florida, took part in the defense of Charleston (1780), and was wounded and captured at Camden in the Carolina campaign. After the war he served as governor (1787–89). While minister to England (1792–96), he was sent as envoy extraordinary to Spain (1794–95). His treaty with Spain (1795) established commercial relations between the United States and Spain, provided for free navigation of the Mississippi by American citizens and Spanish subjects, granted the right of deposit at New Orleans, and set the boundaries of Louisiana and E and W Florida. As a member of Congress (1797–1801) he upheld Federalist measures but voted against the Sedition Act and expressed no eagerness for war with France. In the War of 1812 Pinckney was a major general.
See biography by C. C. Pinckney (1895); S. F. Bemis, Pinckney's Treaty (1960, repr. 1973); J. L. Cross, London Mission (1968).