When the War of 1812 began, he was brigadier general in the New York militia. Though he opposed the war, he organized the defenses in the Great Lakes region. He defeated the British at the Battle of Sackett's Harbor on May 29, 1813. The next year his army captured Fort Erie on Ontario. He was wounded twice at the Battle of Lundy's Lane, one of the bloodiest of the war for both sides. His successes in the northwest made him a national hero.
After the war, the Army was cut and in 1821, he was the only major-general in the service. President James Monroe made him commanding general of the army, but he was unable to do much in the post because of a stroke. He died in Washington, D.C.
The following counties, towns and institutions are named after Jacob Jennings Brown: