Columns: State (class) | Vacator | Reason for change | Successor | Date of successors formal installation
Tennessee (2) | Estes Kefauver (D) | Died August 10, 1963 | Herbert S. Walters (D) | August 20, 1963 | California (1) | Clair Engle (D) | Died July 30, 1964 | Pierre Salinger (D) | August 4, 1964 | South Carolina (2) | Strom Thurmond (D) | Changed political parties | Strom Thurmond (R) | September 16, 1964 | New Mexico (1) | Edwin L. Mechem (R) | Resigned November 3, 1964 | Joseph Montoya (D) | November 4, 1964 | Oklahoma (2) | J. Howard Edmondson (D) | Successor elected November 3, 1964 | Fred R. Harris (D) | November 4, 1964 | Tennessee (2) | Herbert S. Walters (D) | Successor elected November 3, 1964 | Ross Bass (D) | November 4, 1964