This list of members of the United States Congress by longevity of service includes representatives and senators who have served for at least 36 years, in the United States Senate, the United States House of Representatives, or both. In cases where there is a tie in time, the following criteria will sort people higher:

Key

Combined U.S. Senate and U.S. House time

U.S. Senate time

The 90th Congress was notable because for a period of 10 days (December 24, 1968 – January 3, 1969), it contained within the Senate, all 10 of what was at one point the top 10 longest-serving senators in history (Byrd, Inouye, Thurmond, Kennedy, Hayden, Stennis, Stevens, Hollings, Russell Jr., and Long) until January 7, 2013, when Patrick Leahy surpassed Russell B. Long as the 10th longest-serving senator in history. This short 10-day period stretched from the appointment of Ted Stevens of Alaska to fill a vacancy, to the retirement of Carl Hayden of Arizona early the next year. The 107th Congress (2001–2003) was the most recent one to contain the top 7 longest serving senators in history (Byrd, Inouye, Leahy, Thurmond, Kennedy, Grassley, and Hatch). The 99th Congress (1985–1987) and the 100th Congress (1987–1989) were the periods in which most people from this list were serving together (all but Hayden, Russell Jr., Warren, Eastland, Magnuson, and Shelby in the former and all but Hayden, Russell Jr., Long, Warren, Eastland, and Magnuson in the latter).

U.S. House time