He was admitted to the
bar in 1813 and began practicing law in
Glasgow, Kentucky. Underwood served among Glasgow's town trustees and as county auditor until 1823. He was a member of the
Kentucky House of Representatives from 1816 to 1819. In 1823, he moved to
Bowling Green, Kentucky, and again was elected to the State House of Representatives, serving from 1825 to 1826. He ran unsuccessfully for
lieutenant governor of Kentucky in 1828, then served as a judge of the
Court of Appeals from 1828 until 1835, following the
Old Court-New Court controversy. An opponent of
Andrew Jackson and outspoken emancipationist, Underwood was elected as a
Whig to the
United States House of Representatives, serving
Kentucky's District 3 from March 4, 1835, until March 3, 1843. There he was chairman of the
U.S. House Committee on the District of Columbia. He declined to be a candidate for renomination in 1843, and resumed the practice of law. He was a presidential elector on the Whig ticket in 1844, and voters again elected him to the State House in 1846, where he served as speaker. Underwood was elected as a
Whig to the
United States Senate and served from March 4, 1847, to March 3, 1853, when he did not run for reelection. Underwood manumitted his slaves and sent them to
Liberia, he also urged others to do likewise, although he supported the
Compromise of 1850. Before the
American Civil War, Underwood campaigned in Kentucky for the
Constitutional Union Party. He inherited seven slaves in 1858 when his older cousin died however he immediately manumitted them as well. He wanted slavery to end, but also favored a form of gradual emancipation rather than immediate emancipation. He did not believe the federal government had the authority to impose slavery-related laws on states according to the constitution, but was opposed to secession. He ran for the state legislature again and was elected, serving two more terms, from 1861 to 1863 and fighting secessionists in the border state legislature. However, two of his sons would support the Confederacy. He attended the Democratic National Convention in 1864 and helped rebuild that party in the state. During the civil war he was a "strong Union sympathizer" and was outspoken about his support for the union. ==Death and legacy==