St. Clair, Arthur (1736?–1818), an American Revolutionary War general and public official. His career was marked by a series of military and political controversies.

St. Clair was born in Scotland. After joining the British army in 1757, he fought in Canada against the French, at Louisbourg (1758) and at Quebec (1759). In 1762 he left the British army and settled on an estate in western Pennsylvania.

When the Revolutionary War began, St. Clair entered the Continental Army. He served under George Washington, 1776–77. In 1777 St. Clair, then a major general, was placed in command of strategically important Fort Ticonderoga on Lake Champlain. His evacuation of the fort before advancing British forces led to his court-martial in 1778. He was exonerated, but for the remainder of the war he held only minor posts.

St. Clair entered politics as a Federalist. He was a member of the Continental Congress, 1785–87, and became its president in 1787. In 1788 he was appointed governor of the Northwest Territory. As commander of the frontier militia in the territory, he suffered a disastrous defeat at the hands of a smaller Indian force near Fort Wayne in 1791. Although Congress, which investigated the defeat, found him blameless, he resigned from the army. In 1802 he was removed as governor because his opposition to statehood for the territory conflicted with the views of President Jefferson. St. Clair then returned to his Pennsylvania estate. Through generous but unwise lending of his money, he lost most of his wealth. He spent his final years in poverty and political obscurity.