St. Clair, Arthur, 1734–1818, American general, b. Thurso, Scotland. He left the Univ. of Edinburgh to become (1757) an ensign in the British army and served in the French and Indian War at Louisburg and Quebec. In 1762 he resigned his commission and settled in Pennsylvania, where he purchased a vast estate and held a number of civil offices. In the American Revolution he served in the expedition to Canada as colonel of a regiment of militia which he had raised (1775). He was made a brigadier general and, authorized by George Washington to organize the New Jersey militia, fought in the battles of Trenton and Princeton. As major general, St. Clair took command (1777) at Fort Ticonderoga, which he evacuated without a fight to superior British forces. A court-martial in 1778 cleared him of blame, and he served afterward in several minor capacities. After serving as a delegate to Congress (1785–87), St. Clair was appointed (1787) the first governor of the Northwest Territory. He established its capital at Cincinnati and became (1791) commander in chief of the forces fighting the Native Americans. The Native Americans, led by Little Turtle, surprised and defeated St. Clair near the Miami villages. The defeat led him to resign his commission (1792), although a congressional investigating committee later exonerated him. St. Clair's arbitrary rule as governor gained him many enemies, and in 1802 he was removed by Thomas Jefferson after condemning the act making Ohio a state. He published in 1812 a defense of his military conduct and spent his later years in poverty.
See W. H. Smith, ed., The St. Clair Papers (2 vol., 1882, repr. 1971); biography by F. E. Wilson (1944).