The United States Senate, according to the United States Constitution, (Article I), is required to choose a President Pro Tempore (or, "president for a time," often shortened to President Pro Tem), who presides over the Senate in the absence of the Vice President. Because of the smaller size of the Senate and because Senate rules of procedure give more power to individual senators, the President Pro Tem is not a powerful position especially in comparison to the Speaker of the House of Representatives or even the party leaders of the Senate.

In earlier times, when the Vice President usually presided over the Senate, a President pro tempore was chosen each time there was an absence. Since 1890, a sitting president pro tempore has been chosen at the beginning of the session. In 1945, the 79th Congress instituted the custom of giving the position to the longest-serving Senator from the majority party, which has prevailed since. Since the chairmanship of Senate committees is also determined by seniority and this is a more effective means for a Senator to exert influence, most days the Senate is in session it is a junior Senator designated by the President Pro Tem who actually calls the Senate to order with a request that his letter of designation be read.

Since 1947, the President Pro Tempore of the Senate has been third in line to succeed to the US presidency in the case of death or resignation, after the Vice-President and the Speaker of the House of Representatives.

The current President Pro Tempore of the Senate is Ted Stevens of Alaska. Before the Republicans regained control of the Senate after the congressional elections of November 5, 2002, the President Pro Tempore was Robert Byrd of West Virginia. Prior to the shift of James Jeffords from Republican to Independent in May 2001, which shifted control of the Senate from the Republican to the Democratic Party, the office was held by J. Strom Thurmond of South Carolina.

Presidents pro Tempore of the United States Senate

1st Congress (1789-1791)

• John Langdon (NH) April 6 - April 21, 1789
• John Langdon (NH) August 7 - August 9, 1789

2nd Congress (1791-1793)

• Richard Henry Lee (VA) April 18 - October 8, 1792
• John Langdon (NH) November 5 - December 4, 1792
• John Langdon (NH) March 1 - March 3, 1793

3rd Congress (1793-1795)

• John Langdon (NH) March 4 - December 2, 1793
• Ralph Izard (SC) May 31 - November 9, 1794
• Henry Tazewell (VA) February 20 - June 7, 1795

4th Congress (1795-1797)

• Henry Tazewell (Republican-VA) December 7 - December 8, 1795
• Samuel Livermore (Federalist-NH) May 6 - December 4, 1796
• William Bingham (Federalist-PA) February 16 - March 3, 1797

5th Congress (1797-1799)

• William Bradford (Federalist-RI) July 6 - October, 1797
• Jacob Read (Federalist-SC) November 22 - December 12, 1797
• Theodore Sedgwick (Federalist-MA) June 27 - December 5, 1798
• John Laurance (Federalist-NY) December 6 - December 27, 1798
• James Ross (Federalist-PA) March 1 - December 1, 1799

6th Congress (1799-1801)

• Samuel Livermore (Federalist-NH) December 2 - December 29, 1799
• Uriah Tracy (Federalist-CT) May 14 - November 16, 1800
• John E. Howard (Federalist-MD) November 21 - November 27, 1800
• James Hillhouse (Federalist-CT) February 28 - March 3, 1801

7th Congress (1801-1803)

• Abraham Baldwin (Republican-GA) December 7, 1801 - January 14, 1802
• Abraham Baldwin (Republican-GA) April 17 - December 13, 1802
• Stephen R. Bradley (Republican-VT) December 14, 1802 - January 18, 1803
• Stephen R. Bradley (Republican-VT) February 25, 1803
• Stephen R. Bradley (Republican-VT) March 2 - October 16, 1803

8th Congress (1803-1805)

• John Brown (Republican-KY) October 17 - December 6, 1803
• John Brown (Republican-KY) January 23 - February 26, 1804
• Jesse Franklin (Republican-KY) March 10 - November 4, 1804
• Joseph Anderson (Republican-TN) January 15 - February 3, 1805
• Joseph Anderson (Republican-TN) February 28 - March 2, 1805
• Joseph Anderson (Republican-TN) March 2 - December 1, 1805

9th Congress (1805-1807)

• Samuel Smith (Republican-MD) December 2 - December 15, 1805
• Samuel Smith (Republican-MD) March 18 - November 30, 1806
• Samuel Smith (Republican-MD) March 2 - October 25, 1807

10th Congress (1807-1809)

• Samuel Smith (Republican-MD) April 16 - November 6, 1808
• Stephen R. Bradley (Republican-VT) December 28, 1808 - January 8, 1809
• John Milledge (Republican-GA) January 30 - March 3, 1809

11th Congress (1809-1811)

• John Milledge (Republican-GA) March 4 - May 21, 1809
• Andrew Gregg (Republican-PA) June 26 - December 18, 1809
• John Gaillard (Republican-SC) February 28 - March 2, 1810
• John Gaillard (Republican-SC) April 17 - December 11, 1810
• John Pope (Republican-KY) February 23 - November 3, 1811

12th Congress (1811-1813)

• William H. Crawford (Republican-GA) March 24, 1812 - March 3, 1813

13th Congress (1813-1815)

• William H. Crawford (Republican-GA) March 4 - March 23, 1813
• Joseph B. Varnum (Republican-MA) December 6, 1813 - February 3, 1814
• John Gaillard (Republican-SC) November 25, 1814 - December 3, 1815

14th Congress (1815-1817)

• John Gaillard (Republican-SC) December 4, 1815 - March 3, 1817

15th Congress (1817-1819)

• John Gaillard (Republican-SC) March 4, 1817
• John Gaillard (Republican-SC) March 6, 1817 - February 18, 1818
• John Gaillard (Republican-SC) March 31, 1818 - January 5, 1819
• James Barbour (Republican-VA) February 15 - December 5, 1819

16th Congress (1819-1821)

• James Barbour (Republican-VA) December 6 - December 26, 1819
• John Gaillard (Republican-SC) January 25, 1820 - December 2, 1821

17th Congress (1821-1823)

• John Gaillard (Republican-SC) December 3 - December 27, 1821
• John Gaillard (Republican-SC) February 1 - December 2, 1822
• John Gaillard (Republican-SC) February 19 - November 30, 1823

18th Congress (1823-1825)

• John Gaillard (Republican-SC) December 1, 1823 - January 20, 1824
• John Gaillard (Republican-SC) May 21, 1824 - March 3, 1825

19th Congress (1825-1827)

• John Gaillard (Republican-SC) March 9 - December 4, 1825
• Nathaniel Macon (Republican-NC) May 20 - December 3, 1826
• Nathaniel Macon (Republican-NC) January 2 - February 13, 1827
• Nathaniel Macon (Republican-NC) March 2 - December 2, 1827

20th Congress (1827-1829)

• Samuel Smith (Jacksonian-MD) May 15 - December 18, 1828

21st Congress (1829-1831)

• Samuel Smith (Democrat-MD) March 13 - December 10, 1829
• Samuel Smith (Democrat-MD) May 20 - December 31, 1830
• Samuel Smith (Democrat-MD) March 1 - December 4, 1831

22nd Congress (1831-1833)

• Samuel Smith (Democrat-MD) December 5 - December 11, 1831
• Littleton Tazewell (Democrat-MD) July 9 - July 16, 1832
• Hugh L. White (Democrat-TN) December 3, 1832 - December 1, 1833

23rd Congress (1833-1835)

• Hugh L. White (Democrat-TN) December 2 - December 15, 1833
• George Poindexter (Whig-MS) June 28 - November 30, 1834
• John Tyler (Whig-VA) March 3 - December 6, 1835

24th Congress (1835-1837)

• William R. King (Democrat-AL) July 1 - December 4, 1836
• William R. King (Democrat-AL) January 28 - March 3, 1837

25th Congress (1837-1839)

• William R. King (Democrat-AL) March 7 - September 3, 1837
• William R. King (Democrat-AL) October 13 - December 3, 1837
• William R. King (Democrat-AL) July 2 - December 18, 1838
• William R. King (Democrat-AL) February 25 - December 1, 1839

26th Congress (1839-1841)

• William R. King (Democrat-AL) December 2 - December 26, 1839
• William R. King (Democrat-AL) July 3 - December 15, 1840
• William R. King (Democrat-AL) March 3, 1841

27th Congress (1841-1843)

• William R. King (Democrat-AL) March 4, 1841
• Samuel Southard (Whig-NJ) March 11 - May 31, 1842
• Willie P. Mangum (Whig-NC) May 31, 1842 - December 3, 1843

28th Congress (1843-1845)

• Willie P. Mangum (Whig-NC) December 4, 1843 - March 3, 1845

29th Congress (1845-1847)

• Willie P. Mangum (Whig-NC) March 4, 1845
• Ambrose H. Sevier (Democrat-AR) December 27, 1845
• David R. Atchison (Democrat-MO) August 8 - December 6, 1846
• David R. Atchison (Democrat-MO) January 11 - January 13, 1847
• David R. Atchison (Democrat-MO) March 3 - December 5, 1847

30th Congress (1847-1849)

• David R. Atchison (Democrat-MO) February 2 - February 8, 1848
• David R. Atchison (Democrat-MO) June 1 - June 14, 1848
• David R. Atchison (Democrat-MO) June 26 - June 29, 1848
• David R. Atchison (Democrat-MO) July 29 - December 4, 1848
• David R. Atchison (Democrat-MO) December 26, 1848 - January 1, 1849
• David R. Atchison (Democrat-MO) March 2 - March 4, 1849

31st Congress (1849-1851)

• David R. Atchison (Democrat-MO) March 5, 1849
• David R. Atchison (Democrat-MO) March 16 - December 2, 1849
• William R. King (Democrat-AL) May 6 - May 19, 1850
• William R. King (Democrat-AL) July 11, 1850 - March 3, 1851

32nd Congress (1851-1853)

• William R. King (Democrat-AL) March 4, 1851 - December 20, 1852
• David R. Atchison (Democrat-MO) December 20, 1852 - March 3, 1853

33rd Congress (1853-1855)

• David R. Atchison (Democrat-MO) March 4, 1853 - December 4, 1854
• Lewis Cass (Democrat-MI) December 4, 1854
• Jesse D. Bright (Democrat-IN) December 5, 1854 - December 2, 1855

34th Congress (1855-1857)

• Jesse D. Bright (Democrat-IN) December 3, 1855 - June 9, 1856
• Charles E. Stuart (Democrat-MI) June 9 - June 10, 1856
• Jesse D. Bright (Democrat-IN) June 11, 1856 - January 6, 1857
• James M. Mason (Democrat-VA) January 6 - March 3, 1857

35th Congress (1857-1859)

• James M. Mason (Democrat-VA) March 4, 1857
• Thomas J. Rusk (Democrat-TX) March 14 - July 29, 1857
• Benjamin Fitzpatrick (Democrat-AL) December 7 - December 20, 1857
• Benjamin Fitzpatrick (Democrat-AL) March 29 - May 2, 1858
• Benjamin Fitzpatrick (Democrat-AL) June 14 - December 5, 1858
• Benjamin Fitzpatrick (Democrat-AL) January 19, 1859
• Benjamin Fitzpatrick (Democrat-AL) January 25 - February 9, 1859

36th Congress (1859-1861)

• Benjamin Fitzpatrick (Democrat-AL) March 9 - December 4, 1859
• Benjamin Fitzpatrick (Democrat-AL) December 19, 1859 - January 15, 1860
• Benjamin Fitzpatrick (Democrat-AL) February 20 - February 26, 1860
• Jesse D. Bright (Democrat-IN) June 12 - June 13, 1860
• Benjamin Fitzpatrick (Democrat-AL) June 26 - December 2, 1860
• Solomon Foot (Republican-VT) February 16 - February 17, 1861

37th Congress (1861-1863)

• Solomon Foot (Republican-VT) March 23 - July 3, 1861
• Solomon Foot (Republican-VT) July 18 - December 1, 1861
• Solomon Foot (Republican-VT) January 15, 1862
• Solomon Foot (Republican-VT) March 31 - May 21, 1862
• Solomon Foot (Republican-VT) June 19 - December 12, 1862
• Solomon Foot (Republican-VT) February 18 - March 3, 1863

38th Congress (1863-1865)

• Solomon Foot (Republican-VT) March 4 - December 6, 1863
• Solomon Foot (Republican-VT) December 18 - December 20, 1863
• Solomon Foot (Republican-VT) February 23, 1864
• Solomon Foot (Republican-VT) March 11 - March 13, 1864
• Solomon Foot (Republican-VT) April 11 - April 13, 1864
• Daniel Clark (Republican-NH) April 26, 1864 - January 4, 1865
• Daniel Clark (Republican-NH) February 9 - February 19, 1865

39th Congress (1865-1867)

• Lafayette S. Foster (Republican-CT) May 7, 1865 - March 2, 1867
• Benjamin F. Wade (Republican-OH) March 2 - March 3, 1867

40th Congress (1867-1869)

• Benjamin F. Wade (Republican-OH) March 4, 1867 - March 3, 1869

41st Congress (1869-1871)

• Henry B. Anthony (R-RI) March 23-28, 1869
• Henry B. Anthony (R-RI) April 9-December 5, 1869
• Henry B. Anthony (R-RI) May 28-June 2, 1870
• Henry B. Anthony (R-RI) July 1-5, 1870
• Henry B. Anthony (R-RI) July 14-December 4, 1870

42nd Congress (1871-1873)

• Henry B. Anthony (R-RI) March 10-12, 1871
• Henry B. Anthony (R-RI) April 17-May 9, 1871
• Henry B. Anthony (R-RI) May 23-December 3, 1871
• Henry B. Anthony (R-RI) December 21, 1871 - January 7, 1872
• Henry B. Anthony (R-RI) February 23-25, 1872
• Henry B. Anthony (R-RI) June 8-December 1, 1872
• Henry B. Anthony (R-RI) December 4-8, 1872
• Henry B. Anthony (R-RI) December 13-15, 1872
• Henry B. Anthony (R-RI) December 20, 1872 - January 5, 1873
• Henry B. Anthony (R-RI) January 24, 1873

43rd Congress (1873-1875)

• Matthew H. Carpenter (R-WI) March 12-13, 1873
• Matthew H. Carpenter (R-WI) March 26-November 30, 1873
• Matthew H. Carpenter (R-WI) December 11, 1873 - December 6, 1874
• Matthew H. Carpenter (R-WI) December 23, 1874 - January 4, 1875
• Henry B. Anthony (R-RI) January 25-31, 1875
• Henry B. Anthony (R-RI) February 15-17, 1875

44th Congress (1875-1877)

• Thomas W. Ferry (R-MI) March 9-10, 1875
• Thomas W. Ferry (R-MI) March 19, 1875 - March 4, 1877

45th Congress (1877-1879)

• Thomas W. Ferry (R-MI) March 5, 1877
• Thomas W. Ferry (R-MI) February 26-March 3, 1878
• Thomas W. Ferry (R-MI) April 17-December 1, 1878
• Thomas W. Ferry (R-MI) March 3-17, 1879

46th Congress (1879-1881)

• Allen G. Thurman (D-OH) April 15-November 30, 1879
• Allen G. Thurman (D-OH) April 7-14, 1880
• Allen G. Thurman (D-OH) May 6-December 5, 1880

47th Congress (1881-1883)

• Thomas F. Bayard (D-DE) October 10-13, 1881
• David Davis (Independent-IL) October 13, 1881-March 3, 1883
• George F. Edmunds (R-VT) March 3-December 2, 1883

48th Congress (1883-1885)

• George F. Edmunds (R-VT) December 3, 1883 - March 3, 1885

49th Congress (1885-1887)

• John Sherman (R-OH) December 7, 1885 - February 26, 1887
• John J. Ingalls (R-KS) February 26-December 4, 1887

50th Congress (1887-1889)

• John J. Ingalls (R-KS) December 5, 1887 - March 3, 1889

51st Congress (1889-1891) - Present

• John J. Ingalls (R-KS) March 17-17, 1889
• John J. Ingalls (R-KS) April 2-December 1, 1889
• John J. Ingalls (R-KS) December 5-10, 1889
• John J. Ingalls (R-KS) February 28-March 18, 1890

At this point, it was decided that presidents pro tempore should serve until a new one was elected. They were as follows:

• John J. Ingalls (R-KS) April 3, 1890 - March 2, 1891
• Charles F. Manderson (R-NE) March 2, 1891 - March 22, 1893
• Isham G. Harris (D-TN) March 22, 1893 - January 7, 1895
• Matt W. Ransom (D-NC) January 7-10, 1895
• Isham G. Harris (D-TN) January 10-March 3, 1895
• William P. Frye (R-ME) February 7, 1896 - April 27, 1911

Upon Frye's death, it proved difficult to elect a successor. For the remainder of the 62nd Congress (1911-1913), the position alternated among:

• Augustus O. Bacon (D-GA)
• Charles Curtis (R-KS)
• Jacob H. Gallinger (R-NH)
• Frank B. Brandegee (R-CT) and
• Henry Cabot Lodge (R-MA)

In the next Congress, things returned to normal:

• James P. Clarke (D-AR) March 13, 1913 - October 1, 1916
• Willard Saulsbury (D-DE) December 14, 1916 - March 3, 1919
• Albert B. Cummins (R-IA) May 19, 1919 - March 6, 1925
• George H. Moses (R-NH) March 6, 1925 - March 3, 1933
• Key Pittman (D-NV) March 9, 1933 - November 10, 1940
• William H. King (D-UT) November 19, 1940 - January 3, 1941
• B. Patton Harrison (D-MS) January 6 - June 22, 1941
• Carter Glass (D-VA) July 10, 1941 - January 2, 1945
• Kenneth McKellar (D-TN) January 6, 1945 - January 2, 1947
• Arthur H. Vandenberg (R-MI) January 4, 1947 - January 2, 1949
• Kenneth McKellar (D-TN) January 3, 1949 - January 2, 1953
• Styles Bridges (R-NH) January 3, 1953 - January 4, 1955
• Walter F. George (D-GA) January 5, 1955 - January 2, 1957
• Carl T. Hayden (D-AZ) January 3, 1957 - January 2, 1969
• Richard B. Russell, Jr. (D-GA) January 3, 1969 - January 21, 1971
• Allen J. Ellender (D-LA) January 22, 1971 - July 27, 1972
• James O. Eastland (D-MS) July 28, 1972 - December 27, 1978
• Warren G. Magnuson (D-WA) January 15, 1979 - December 4, 1980
• Milton R. Young (R-ND) December 5, 1980
• Warren G. Magnuson (D-WA) December 6, 1980 - January 4, 1981
• J. Strom Thurmond (R-SC) January 5, 1981 - January 5, 1987
• John C. Stennis (D-MS) January 6, 1987 - January 2, 1989
• Robert C. Byrd (D-WV) January 3, 1989 - January 3, 1995
• J. Strom Thurmond (R-SC) January 4, 1995 - January 3, 2001
• Robert C. Byrd (D-WV) January 3-20, 2001
• J. Strom Thurmond (R-SC) January 20-June 6, 2001
• Robert C. Byrd (D-WV) June 6, 2001 - January 3, 2003
• Theodore F. Stevens (R-AK) January 3, 2003 - Present