Following his father's death, the 18 year old Harrison was commissioned as an ensign in the US Army. Two years later in 1793 his mother died and Harrison inherited a portion of the family's estate, including about 3,000 acres of land and several slaves.
In 1801, Harrison moved to the Indiana Territory where he was appointed as Governor. In 1803 Harrison lobbied Congress to repeal Article 6 of the Northwest Ordinance, in order to permit slavery in the territory. He argued that it was necessary to make the region more appealing to settlers and would make the territory economically viable. He was able to convince Congress to suspended the article for 10 years, during which time the territories covered by the ordinance were granted the right to decide for themselves whether to permit slavery. Harrison tried to have slavery legalized outright, in both 1805 and 1807. This caused a significant stir in the territory. When in 1809 the legislature was popularly elected for the first time, Harrison found himself at odds with them as the abolitionist party came to power. They immediately blocked his plans for slavery and repealed the indenturing laws he had passed in 1803. President Thomas Jefferson, although a slaveholder, did not want slavery to expand into the Northwest Territory. Anti-slavery churches in Indiana organized citizens to sign a petition and organizing politically to defeat Harrison's efforts to legalize slavery.
Harrison was the Northern Whig candidate for president in 1836, the only time in American history when a major political party intentionally ran more than one presidential candidate. Harrison ran in all the free states except Massachusetts, and the slave states of Delaware, Maryland, and Kentucky. The plan was to prevent Martin Van Buren from winning a majority in the electoral college, but it failed. Harrison ran as the Whig candidate in 1840 and again faced Van Buren, now the incumbent president. Harrison based his campaign on his heroic military record and on the weak U.S. economy, caused by the Panic of 1837. Although Harrison had come from a slaveholding Virginia family, in this campaign he was promoted as a humble frontiersman in the style of the popular Andrew Jackson.
Harrison won election to the Presidency, but served only 31 days in office (the shortest presidency) before his death. In his brief tenure as president, he was unable to effect any policies respecting slavery or civil rights. Based on Harrison's record as Governor of Indiana, slave-holding states probably felt as if they had lost a kindred spirit and a supporter of their cause.