This is a complete list of United States senators during the 117th United States Congress listed by seniority from January 3, 2021, to January 3, 2023. 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, the most junior senior senator was Kelly Loeffler until Jon Ossoff (from the other seat) and Raphael Warnock (Loeffler's successor) were sworn in on January 20, 2021, after which Ossoff became the most junior senior senator. The most senior junior senator is Maria Cantwell.
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 factors are the population of the senator's state and the alphabetical position of the senator's surname.
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.