required by the Constitution.Incumbent was re-elected October 27, 1849, having by then qualified. | | James Shields (D) | Seated December 3, 1849 |- | Maryland(1) | | Reverdy Johnson (W) | Resigned March 7, 1849, having been appointed United States Attorney General | | David Stewart (W) | Appointed December 6, 1849 |- | Alabama(2) | | Benjamin Fitzpatrick (D) | Sen. Dixon Lewis successor elected November 30, 1849 | | Jeremiah Clemens (D) | Elected November 30, 1849 |- | Maryland(1) | | David Stewart (W) | Successor elected January 12, 1850 | | Thomas Pratt (W) | Elected January 12, 1850 |- | South Carolina(2) | | John C. Calhoun (D) | Died March 31, 1850 | | Franklin H. Elmore (D) | Appointed April 11, 1850 |- | South Carolina(2) | | Franklin H. Elmore (D) | Died May 29, 1850 | | Robert W. Barnwell (D) | Appointed June 4, 1850 |- | Ohio(1) | | Thomas Corwin (W) | Resigned July 20, 1850, after being appointed United States Secretary of the Treasury | | Thomas Ewing (W) | Appointed July 20, 1850 |- | Massachusetts(1) | | Daniel Webster (W) | Resigned July 22, 1850, after being appointed United States Secretary of State again. | | Robert C. Winthrop (W) | Appointed July 30, 1850 |- | California(1) | New state | California admitted to the Union September 9, 1850.The first Senator was elected September 10, 1850. | | John C. Frémont (D) | Elected September 10, 1850 |- | California(3) | New state | California admitted to the Union September 9, 1850.The first Senator was elected September 10, 1850. | | William M. Gwin (D) | Elected September 10, 1850 |- | South Carolina(2) | | Robert W. Barnwell (D) | Successor elected December 18, 1850 | | Robert Rhett (D) | Elected December 18, 1850 |- | Massachusetts(1) | | Robert C. Winthrop (W) | Successor elected February 1, 1851 | | Robert Rantoul Jr. (D) | Elected February 1, 1851 |} House of Representatives Replacements: 11 Democrats (D): 2 seat net gain Whigs (W): 2 seat net loss Deaths: 8 Resignations: 5 Contested election:1 Seats from newly admitted states: 2 Total seats with changes: 16 |- | | Vacant | style="font-size:80%" | Seat remained vacant after territory became organized at end of previous congress | Henry H. Sibley | Seated July