After leaving government service, Houston began an apprenticeship with Judge James Trimble in Nashville. He quickly won admission to the state bar and opened a legal practice in Lebanon, Tennessee. With the aid of Governor Joseph McMinn, Houston won election as the district attorney for Nashville in 1819. He was also appointed as a major general of the Tennessee militia. Like his mentors, Houston was a member of the Democratic-Republican Party, which dominated state and national politics in the decade following the War of 1812. Tennessee gained three seats in the United States House of Representatives after the 1820 United States Census, and, with the support of Jackson and McMinn, Houston ran unopposed in the 1823 election for Tennessee's 9th congressional district. In his first major speech in Congress, Houston advocated for the recognition of Greece, which was fighting a war of independence against the Ottoman Empire.