In 1807 Daniel was admitted to the Virginia
bar and began a private legal practice in
Falmouth across the
Rappahannock River from
Fredericksburg. In November 1808, Daniel became involved in a dispute with a Fredericksburg businessman, John Seddon, and both parties agreed to a duel. Since dueling was prohibited in Virginia, the Daniel-Seddon duel was fought in Maryland. Daniel wounded Seddon during the duel, although he himself was unscathed, and Sedden died of his wound shortly after returning to Virginia. The duel did not crimp Daniel's career. In 1809, Stafford County voters elected him to the
Virginia House of Delegates, and re-elected him once, so he served in that part-time position first alongside his relative John Moncure and then with
William Brent. Daniel championed states' rights principles embodied in the Virginia and Kentucky Resolutions of 1798, and promoted agrarian issues and strict construction of the federal Constitution. Daniel moved to Richmond by 1810 and in 1812 his former colleagues elected him to the advisory Virginia Council of State (privy council), and would re-elect him, so he served until 1835, three years after adoption of the Virginia Constitution of 1832. During the 1830s, he was a member of the
Richmond Junto, a powerful group of the
Jacksonian Democrats and slaveholders, and strongly supported both
Andrew Jackson and
Martin Van Buren. Daniel was described as a "personal friend" of Jackson. In 1830, Daniel ran unsuccessfully for governor of Virginia. ==Judicial service==