Source

Senate rank is first determined by the length of consecutive service in the Senate. For senators who entered the Senate on the same day, several tie-breaking procedures determine seniority. In order of precedence, these factors are: previous Senate service, service as the vice president, previous House service; service in the Cabinet, service as a state governor. If a tie still exists, senators are ranked according to the population of their state at the time of swearing in.

1. Patrick J. Leahy, D-VT Jan. 3, 1975
2. Orrin G. Hatch, R-UT Jan. 3, 1977
3. Charles E. Grassley, R-IA Jan. 3, 1981
4. Mitch McConnell, R-KY Jan. 3, 1985
5. Richard C. Shelby, R-AL Jan. 3, 1987
6. Dianne Feinstein, D-CA Nov. 4, 1992
7. Patty Murray, D-WA Jan. 3, 1993
8. James M. Inhofe, R-OK Nov. 16, 1994
9. Ron Wyden, D-OR Feb. 6, 1996
10. Pat Roberts, R-KS Jan. 3, 1997
11. Richard J. Durbin, D-IL Jan. 3, 1997
12. Jack Reed, D-RI Jan. 3, 1997
13. Susan Collins, R-ME Jan. 3, 1997
14. Michael B. Enzi, R-WY Jan. 3, 1997
15. Charles E. Schumer, D-NY Jan. 3, 1999
16. Michael D. Crapo, R-ID Jan. 3, 1999
17. Bill Nelson, D-FL Jan. 3, 2001
18. Thomas R. Carper, D-DE Jan. 3, 2001
19. Debbie Stabenow, D-MI Jan. 3, 2001
20. Maria Cantwell, D-WA Jan. 3, 2001
21. Lisa Murkowski, R-AK Dec. 20, 2002
22. Lindsey Graham, R-SC Jan. 3, 2003
23. Lamar Alexander, R-TN Jan. 3, 2003
24. John Cornyn, R-TX Dec. 2, 2002*
25. Richard M. Burr, R-NC Jan. 3, 2005
26. John Thune, R-SD Jan. 3, 2005
27. Johnny Isakson, R-GA Jan. 3, 2005
28. Robert Menendez, D-NJ Jan. 18, 2006
29. Benjamin L. Cardin, D-MD Jan. 3, 2007
30. Bernie Sanders, I-VT Jan. 3, 2007
31. Sherrod Brown, D-OH Jan. 3, 2007
32. Bob Casey, D-PA Jan. 3, 2007
33. Bob Corker, R-TN Jan. 3, 2007
34. Claire McCaskill, D-MO Jan. 3, 2007
35. Amy Klobuchar, D-MN Jan. 3, 2007
36. Sheldon Whitehouse, D-RI Jan. 3, 2007
37. Jon Tester, D-MT Jan. 3, 2007
38. John A. Barrasso, R-WY June 22, 2007
39. Roger Wicker, R-MS Dec. 31, 2007
40. Tom Udall, D-NM Jan. 3, 2009
41. Jeanne Shaheen, D-NH Jan. 3, 2009
42. Mark Warner, D-VA Jan. 3, 2009
43. Jim Risch, R-ID Jan. 3, 2009
44. Jeff Merkley, D-OR Jan. 3, 2009
45. Michael Bennet, D-CO Jan. 22, 2009
46. Kirsten Gillibrand, D-NY Jan. 27, 2009
47. Joe Manchin, D-WV Nov. 15, 2010
48. Chris Coons, D-DE Nov. 15, 2010
49. Roy Blunt, R-MO Jan. 3, 2011
50. Jerry Moran, R-KS Jan. 3, 2011
51. Rob Portman, R-OH Jan. 3, 2011
52. John Boozman, R-AR Jan. 3, 2011
53. Pat Toomey, R-PA Jan. 3, 2011
54. John Hoeven, R-ND Jan. 3, 2011
55. Marco Rubio, R-FL Jan. 3, 2011
56. Ron Johnson, R-WI Jan. 3, 2011
57. Rand Paul, R-KY Jan. 3, 2011
58. Richard Blumenthal, D-CT Jan. 3, 2011
59. Mike Lee, R-UT Jan. 3, 2011
60. Dean Heller, R-NV May 9, 2011
61. Brian Schatz, D-HI Dec. 27, 2012
62. Tim Scott, R-SC Jan. 3, 2013
63. Tammy Baldwin, D-WI Jan. 3, 2013
64. Jeff Flake, R-AZ Jan. 3, 2013
65. Joe Donnelly, D-IN Jan. 3, 2013
66. Chris Murphy, D-CT Jan. 3, 2013
67. Mazie Hirono, D-HI Jan. 3, 2013
68. Martin Heinrich, D-NM Jan. 3, 2013
69. Angus King, I-ME Jan. 3, 2013
70. Tim Kaine, D-VA Jan. 3, 2013
71. Ted Cruz, R-TX Jan. 3, 2013
72. Elizabeth Warren, D-MA Jan. 3, 2013
73. Deb Fischer, R-NE Jan. 3, 2013
74. Heidi Heitkamp, D-N.D. Jan. 3, 2013
75. Edward Markey, D-MA Jul. 16, 2013
76. Cory Booker, D-NJ Oct. 31, 2013
77. Shelley Moore Capito, R-WV Jan. 3, 2015
78. Gary Peters, D-MI Jan. 3, 2015
79. Bill Cassidy, R-LA Jan. 3, 2015
80. Cory Gardner, R-CO Jan. 3, 2015
81. James Lankford, R-OK Jan. 3, 2015
82. Tom Cotton, R-AR Jan. 3, 2015
83. Steve Daines, R-MT Jan. 3, 2015
84. Mike Rounds, R-SD Jan. 3, 2015
85. David Perdue, R-GA Jan. 3, 2015
86. Thom Tillis, R-NC Jan. 3, 2015
87. Joni Ernst, R-IA Jan. 3, 2015
88. Ben Sasse, R-NE Jan. 3, 2015
89. Dan Sullivan, R-AK Jan. 3, 2015
90. Chris Van Hollen, D-MD Jan 3, 2017
91. Todd Young, R-IN Jan 3, 2017
92. Tammy Duckworth, D-IL Jan 3, 2017
93. Maggie Hassan, D-NH Jan 3, 2017
94. Kamala Harris, D-CA Jan 3, 2017
95. John Kennedy, R-LA Jan 3, 2017
96. Catherine Cortez-Masto, D-NV Jan 3, 2017
97. Tina Smith, D-MN, Jan 3, 2018
98. Doug Jones, D-AL, Jan 3, 2018
99. Cindy Hyde Smith, April 9, 2018
100. Jon Kyl, September 5, 2018

* Phil Gramm resigned early, effective Nov. 30, 2002, so that Cornyn could move into his office suite and begin organizing his staff. Cornyn did not, however, gain seniority, owing to a 1980 Rules Committee policy established by Senator Pell that no longer gave seniority to senators who entered Congress early for the purpose of gaining advantageous office space.