Robert Barnwell Rhett (October 21, 1800-September 14, 1876) was a United States secessionist politician from South Carolina.
Rhett born in Beaufort, South Carolina. His name was originally Smith, but after entering public life he changed it for that of a prominent Colonial ancestor. He studied law and became a member of the State Legislature in 1826.
His posts were those of lawyer, state legislator, state attorney general (1832), U.S. representative (1837-49), and senator (1850-52). Extremely pro-Southern in his views, he split (1844) with John C. Calhoun to lead the movement for separate state action on the tariff. Rhett was one of the leading fire-eaters at the Nashville Convention of 1850, which failed to endorse his aim of secession for the whole South.