Duncan Stewart (1763–1819) was a United States politician, who during his career held offices in three U.S. states: North Carolina, Tennessee and Mississippi and holding a very rare distinction of serving in three different state legislatures (North Carolina House of Representatives, Tennessee House of Representatives and Mississippi House of Representatives).
He is best known as first Lieutenant Governor of Mississippi (1817–1820) serving under Governor David Holmes. He died in this office and is interred at Stewart Two Cemetery, near Woodville, Wilkinson County, Mississippi.
Stewart County, Tennessee is named after him.