This is a complete list of United States senators during the 116th United States Congress listed by seniority from January 3, 2019, to January 3, 2021. 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.
In this Congress, Kyrsten Sinema is the most junior senior senator and Maria Cantwell is the most senior junior senator.
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.
The most senior senators by class were Dianne Feinstein (D-California) from Class 1, Mitch McConnell (R-Kentucky) from Class 2, and Patrick Leahy (D-Vermont) from Class 3.