Attended the College of New Jersey for two years before joining the Continental army (1776). Aide-de-camp to Mercer and Gates.
The anonymous author of the controversial "Newburgh Addresses," intended to pressure Congress into redressing the army's grievances.
Secretary of the Supreme Executive Council of Pennsylvania (1783-87). Adjutant general of Pennsylvania Delegate from Pennsylvania to the Continental Congress (1787-88). United States senator from New York. Minister to France (1804-10). Minister to Spain (1806). Secretary of War under Madison (1813-14). Author of various pamphlets and of the two volume Notices of the War of 1812.
Born in Carlisle, Cumberland County, Pennsylvania. Son of John Armstrong. Married in 1789 to Alida Livingston, sister of Robert Livingston, and settled in New York.