He entrance into the military life was a disappointment to his father as he wanted William to become a doctor. During the War of 1812, Harrison fought a combined British and Indian force of 1,700 men in the battle at the Thames River in 1813. While he was in the Northwestern Army, and after he was promoted to major general he showed a concern in fortifying Fort Meigs at the Maumee Rapids to withstand two sieges by the British and Indians. The Battle of Tippecanoe, upon which made Harrison's name a household word he fought against Tecumseh's confederacy but failed to diminish Indian raids. In the War of 1812 Harrison had more military victories when he was given the command of the Army in the Northwest. After resigning from the Army in he became the Secretary of the Northwest Territory to which he remained there for 13 years.

A few Indian treaties made by Harrison opened a new area for settlement. With the Treaty of Fort Wayne the Delaware, Miami, Potawatomi, and Eel Indians gave up about 3 million acres in return for annual payment ranging from $200 to $500 to each tribe. He made a very long inaugural address on March 4, 1841 in an extremely cold day and did not wear a hat while delivering the 105 minute speech. He caught pneumonia and expired in the White House one month later. Up to that time he was the first president to die in office. In his campaign he sought support from war veterans with whom he fought. When elected he carried 19 of the 26 states, winning an electoral total of 234. He was the first president elected from the Whig Party.