This is a complete list of United States senators during the 118th United States Congress listed by seniority from January 3, 2023, to January 3, 2025. It is a historical listing and will contain people who have not served the entire two-year Congress should anyone resign, die, or be expelled.
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. If two senators are tied on all factors, as in the case of Jon Ossoff and Raphael Warnock, the senator elected to the full term is the senior senator.
In this Congress, the most junior senior senator is Jon Ossoff, and Maria Cantwell is the most senior junior senator.
The most senior senators by class were Dianne Feinstein (D-California) from Class 1, Mitch McConnell (R-Kentucky) from Class 2, and Chuck Grassley (R-Iowa) from Class 3. When Feinstein died on September 29, 2023 Tom Carper (D-Delaware) became the most senior senator from his class.