Born in Sinnepuxent, Maryland, 5 January 1779. Appointed Midshipman US Navy, 30 April 1798. He served on the USS United States during the 1798-1799 War with France. He captured the USS Philadelphia from the Tripolitans, in the harbor of Tripoli, and destroyed her. In the War of 1812 he captured the HMS Macedonian while in command of USS United States. In the spring of 1814 he commanded the President and a squadron of three vessels, when he had a severe engagement with the British West India Squadron.
He surrendered after having lost a quarter of the crew and was surrounded by three frigates. Decatur was made prisoner, taken to Bermuda, and from there sent to the frigate HMS Narcissus. After peace was declared with Great Britain he was freed and returned to secure the final treaty of peace with the Barbary Powers. From 1816 to 1820 he was the Navy Commissioner, and he received a gold medal for distinguished service in the War of 1812. His death resulted from a duel with Commodore Barron. His remains were temporarily deposited in the tomb of Joel Barlow at Washington, but later moved to Philadelphia.