The 3rd Mississippi Legislature (then known as the Mississippi General Assembly) met from January 3 to February 12, 1820, in Natchez, Mississippi.
The Mississippi State Senate was composed of the following. Joseph Johnson was elected President pro tempore of the Senate. James Patton took office as Lieutenant Governor of Mississippi on January 5, 1820, and became the ex officio President of the Mississippi State Senate.
The Mississippi House of Representatives was composed of the following. Edward Turner was elected Speaker of the House. Non-representatives Peter A. Vandorn and William Mason were elected to the offices of clerk and doorkeeper, respectively.