Columns: District | Vacator | Reason for change | Successor | Date successor seated
California 23rd | Clyde Doyle (D) | Died March 14, 1963 | Del M. Clawson (R) | June 11, 1963 | Pennsylvania 15th | Francis E. Walter (D) | Died May 31, 1963 | Fred B. Rooney (D) | July 30, 1963 | North Dakota 1st | Hjalmar C. Nygaard (R) | Died July 18, 1963 | Mark Andrews (R) | October 22, 1963 | Pennsylvania 23rd | Leon H. Gavin (R) | Died September 15, 1963 | Albert W. Johnson (R) | November 3, 1963 | Pennsylvania 5th | William J. Green, Jr. (D) | Died December 21, 1963 | William J. Green, III (D) | April 28, 1964 | Tennessee 2nd | Howard Baker, Sr. (R) | Died January 7, 1964 | Irene Baker (R) | March 10, 1964 | Illinois 6th | Thomas J. O'Brien (D) | Died April 14, 1964 | Vacant | Not filled this term | Missouri 9th | Clarence Cannon (D) | Died May 12, 1964 | William L. Hungate (D) | November 3, 1964 | Michigan 12th | John B. Bennett (R) | Died August 9, 1964 | Vacant | Not filled this term