A special election was held in South Carolina's 6th congressional district June 1–2, 1807 to fill a vacancy left by the death of Levi Casey (DR) on February 3, 1807.
Casey had been elected for a third term to the 10th United States Congress in the 1806 elections. His death left a vacancy for the remainder of the 9th Congress, which remained unfilled, as well as for the 10th Congress.
South Carolina's 6th congressional district special election, 1807 Wikipedia
Calhoun took his seat October 26, 1807, at the start of the 1st session of the 10th Congress.