This is a complete list of United States senators during the 80th United States Congress listed by seniority from January 3, 1947, to January 3, 1949.
Order of service is based on the commencement of the senator's first term. Behind this is former service as a senator (only giving the senator seniority within their new incoming class), service as vice president, a House member, a cabinet secretary, or a governor of a state. The final factor is the population of the senator's state.
Senators who were sworn in during the middle of the two-year congressional term (up until the last senator who was not sworn in early after winning the November 1948 election) are listed at the end of the list with no number.
In this congress, Richard Russell Jr. was the most senior junior senator and Leverett Saltonstall was the junior senior senator.
The most senior senators by class were Kenneth McKellar (D-Tennessee) from Class 1, Arthur Capper (R-Kansas) from Class 2, and Walter F. George (D-Georgia) from Class 3.