Langdon, John, 1741–1819, American political leader, b. Portsmouth, N.H. A prosperous merchant, Langdon was active in pre-Revolutionary activities. In 1775 he became a delegate to the Continental Congress, and in Nov., 1775, he accompanied Robert R. Livingston and Robert Treat Paine on an unsuccessful mission to win Canada to the patriot cause. In the Saratoga campaign (1777) he financed the New Hampshire militia under Gen. John Stark in the expedition against General Burgoyne, and he saw action himself at Bennington and Saratoga. After the war he was (1785–86, 1788–89) president (governor) of New Hampshire. Langdon was a delegate to the U.S. Constitutional Convention, and it was largely through his efforts that New Hampshire ratified the Constitution as the ninth state, thus making the instrument effective. As U.S. Senator (1789–1801) he aligned himself more and more with the Jeffersonians, but he declined national offices. Langdon was governor of New Hampshire from 1805 to 1809 and from 1810 to 1812.
See biography by L. S. Mayo (1937, repr. 1970).