Immigrated to Philadelphia (1771), where he studied medicine with Benjamin Rush. Surgeon in the Continental Army (1776). Assistant secretary to George Washington (1778). Aide- de-camp to the marquis de Lafayette (1780). Member of the Maryland Assembly (1788-91), the Maryland Senate (1781-86, 1791-96), and the U.S. Congress (1783-85). Maryland delegate to the Constitutional Convention (1787). Secretary of War (1796-1800). Federalist.
Son of Daniel and Agnes McHenry of Ballymena, Ireland. Married Margaret Caldwell (1784); four children.
First letter in correspondence: August 24, 1784; DAB; John A. Garraty and Mark C. Carnes, American National Biography (24 vols., New York, 1999).