This is a complete list of United States senators during the 75th United States Congress listed by seniority from January 3, 1937, to January 3, 1939.
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 Congress (up until the last senator who was not sworn in early after winning the November 1938 election) are listed at the end of the list with no number.
In this Congress, the most senior junior senator was Gerald Nye. The most junior senior senator was Charles Andrews until January 17, 1938, after which it was William Smathers.
The most senior senators by class were Henry F. Ashurst (R-Arizona) from Class 1, William Borah (R-Idaho) from Class 2, and Ellison D. Smith (D-South Carolina) from Class 3.