| Class 1Class 1 U.S. senators belong to the electoral cycle that has recently been contested in2006,2012,2018, and2024. The next election will be in2030. | C | Class 3Class 3 U.S. senators belong to the electoral cycle that has recently been contested in2004,2010,2016, and2022. The next election will be in2028. |
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| # | Senator | Party | Dates in office | Electoral history | T | T | Electoral history | Dates in office | Party | Senator | # |
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| 1 |  William Maclay | Anti- Admin. | Mar 4, 1789 – Mar 3, 1791 | Elected in 1788.Lost re-election. | 1 | 1st | 1 | Elected in 1788.Retired. | Mar 4, 1789 – Mar 3, 1795 | Pro- Admin. |  Robert Morris | 1 |
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| Vacant | Mar 4, 1791 – Dec 1, 1793 | Legislature failed to elect. | 2 | 2nd |
| 2 |  Albert Gallatin | Anti- Admin. | Dec 2, 1793 – Feb 28, 1794 | Elected to finish the vacant term.Election voided. |
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| 3rd |
| Vacant | Mar 1, 1794 – Apr 23, 1794 | |
| 3 |  James Ross | Pro- Admin. | Apr 24, 1794 – Mar 3, 1803 | Elected to finish the vacant term that happened from 1791 to 1793. |
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| Federalist | 4th | 2 | Elected in 1795.Retired. | Mar 4, 1795 – Mar 3, 1801 | Federalist |  William Bingham | 2 |
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| Re-elected in 1797.Retired. | 3 | 5th |
| 6th |
| 7th | 3 | Elected in 1801.Resigned to become Supervisor of Revenue of Pennsylvania. | Mar 4, 1801 – Jun 30, 1801 | Democratic- Republican |  Peter Muhlenberg | 3 |
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| | Jun 30, 1801 – Dec 17, 1801 | Vacant |
| Elected to finish Muhlenberg's term.Retired. | Dec 17, 1801 – Mar 3, 1807 | Democratic- Republican |  George Logan | 4 |
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| 4 | Samuel Maclay | Democratic- Republican | Mar 4, 1803 – Jan 4, 1809 | Elected in 1802.Resigned. | 4 | 8th |
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| 9th |
| 10th | 4 | Elected in 1806.Retired. | Mar 4, 1807 – Mar 3, 1813 | Democratic- Republican |  Andrew Gregg | 5 |
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| Vacant | Jan 4, 1809 – Jan 9, 1809 | Vacant |
| 5 |  Michael Leib | Democratic- Republican | Jan 9, 1809 – Feb 14, 1814 | Elected in 1809 to finish Maclay's term, having been elected to the next term.[1] |
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| Elected in 1808.[2]Resigned to become Postmaster of Philadelphia. | 5 | 11th |
| 12th |
| 13th | 5 | Elected in 1812.[3]Retired. | Mar 4, 1813 – Mar 3, 1819 | Democratic- Republican |  Abner Lacock | 6 |
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| Vacant | Feb 14, 1814 – Feb 24, 1814 | |
| 6 |  Jonathan Roberts | Democratic- Republican | Feb 24, 1814 – Mar 3, 1821 | Elected to finish Leib's term. |
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| Re-elected in late 1814. | 6 | 14th |
| 15th |
| 16th | 6 | Elected in 1818.Retired. | Mar 4, 1819 – Mar 3, 1825 | Democratic- Republican |  Walter Lowrie | 7 |
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| Vacant | Mar 4, 1821 – Dec 10, 1821 | Legislature failed to elect. | 7 | 17th |
| 7 |  William Findlay | Democratic- Republican | Dec 10, 1821 – Mar 3, 1827 | Elected late in 1821.Retired. |
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| 18th |
| Jacksonian | 19th | 7 | Elected in 1825.Lost re-election. | Mar 4, 1825 – Mar 3, 1831 | National Republican |  William Marks | 8 |
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| 8 |  Isaac D. Barnard | Jacksonian | Mar 4, 1827 – Dec 6, 1831 | Elected in 1826.Resigned to due ill health. | 8 | 20th |
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| 21st |
| 22nd | 8 | Elected in 1830.Resigned to becomeU.S. Minister to Russia. | Mar 4, 1831 – Jun 30, 1834 | Jacksonian |  William Wilkins | 9 |
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| Vacant | Dec 6, 1831 – Dec 13, 1831 | |
| 9 |  George M. Dallas | Jacksonian | Dec 13, 1831 – Mar 3, 1833 | Elected to finish Barnard's term.Retired. |
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| Vacant | Mar 4, 1833 – Dec 7, 1833 | Legislature failed to elect. | 9 | 23rd |
| 10 |  Samuel McKean | Jacksonian | Dec 7, 1833 – Mar 3, 1839 | Elected late in 1833. |
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| | Jun 30, 1834 – Dec 6, 1834 | Vacant |
| Elected to finish Wilkins's term. | Dec 6, 1834 – Mar 5, 1845 | Jacksonian |  James Buchanan | 10 |
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| 24th |
| Democratic | 25th | 9 | Re-elected in 1836. | Democratic |
| Vacant | Mar 4, 1839 – Jan 14, 1840 | Legislature failed to elect. | 10 | 26th |
| 11 |  Daniel Sturgeon | Democratic | Jan 14, 1840 – Mar 3, 1851 | Elected late in 1840. |
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| 27th |
| 28th | 10 | Re-elected in 1843.Resigned to becomeU.S. Secretary of State. |
| Re-elected in 1845.Retired. | 11 | 29th |
| | Mar 5, 1845 – Mar 13, 1845 | Vacant |
| Elected in 1845 to finish Buchanan's term.Retired. | Mar 13, 1845 – Mar 3, 1849 | Democratic |  Simon Cameron | 11 |
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| 30th |
| 31st | 11 | Elected in 1849. | Mar 4, 1849 – Mar 3, 1855 | Whig |  James Cooper | 12 |
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| 12 |  Richard Brodhead | Democratic | Mar 4, 1851 – Mar 3, 1857 | Elected in 1851. | 12 | 32nd |
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| 33rd |
| 34th | 12 | Legislature failed to elect. | Mar 4, 1855 – Jan 14, 1856 | Vacant |
| Elected late in 1856.Retired. | Jan 14, 1856 – Mar 3, 1861 | Democratic |  William Bigler | 13 |
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| 13 |  Simon Cameron | Republican | Mar 4, 1857 – Mar 4, 1861 | Elected in 1857.Resigned to becomeU.S. Secretary of War. | 13 | 35th |
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| 36th |
| Vacant | Mar 4, 1861 – Mar 14, 1861 | | 37th | 13 | Elected in 1861.Lost re-election. | Mar 4, 1861 – Mar 3, 1867 | Republican |  Edgar Cowan | 14 |
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| 14 |  David Wilmot | Republican | Mar 14, 1861 – Mar 3, 1863 | Elected in 1861 to finish Cameron's term.Retired. |
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| 15 |  Charles R. Buckalew | Democratic | Mar 4, 1863 – Mar 3, 1869 | Elected in 1863. | 14 | 38th |
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| 39th |
| 40th | 14 | Elected in 1867. | Mar 4, 1867 – Mar 12, 1877 | Republican |  Simon Cameron | 15 |
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| 16 |  John Scott | Republican | Mar 4, 1869 – Mar 3, 1875 | Elected in 1869.Retired. | 15 | 41st |
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| 42nd |
| 43rd | 15 | Re-elected in 1873.Resigned. |
| 17 |  William A. Wallace | Democratic | Mar 4, 1875 – Mar 3, 1881 | Elected in 1875.Lost re-election. | 16 | 44th |
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| 45th |
| | Mar 12, 1877 – Mar 20, 1877 | Vacant |
| Elected in 1877 to finish his father's term. | Mar 20, 1877 – Mar 3, 1897 | Republican |  J. Donald Cameron | 16 |
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| 46th | 16 | Re-elected in 1879. |
| 18 |  John I. Mitchell | Republican | Mar 4, 1881 – Mar 3, 1887 | Elected in 1881. | 17 | 47th |
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| 48th |
| 49th | 17 | Re-elected in 1885. |
| 19 |  Matthew Quay | Republican | Mar 4, 1887 – Mar 3, 1899 | Elected in early 1887. | 18 | 50th |
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| 51st |
| 52nd | 18 | Re-elected in 1891.Retired. |
| Re-elected in 1893.Legislature failed to re-elect. | 19 | 53rd |
| 54th |
| 55th | 19 | Elected in 1897. | Mar 4, 1897 – Dec 31, 1921 | Republican |  Boies Penrose | 17 |
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| Vacant | Mar 4, 1899 – Jan 16, 1901 | Quay was appointed to continue the term, but the Senate rejected his appointment. | 20 | 56th |
 Matthew Quay | Republican | Jan 16, 1901 – May 28, 1904 | Elected late in 1901.Died. |
| 57th |
| 58th | 20 | Re-elected in 1903. |
| 20 |  Philander C. Knox | Republican | Jun 10, 1904 – Mar 3, 1909 | Appointed to continue Quay's term.Elected in 1905 to finish Quay's term.[4] |
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| Re-elected in 1905.[5]Resigned to becomeU.S. Secretary of State. | 21 | 59th |
| 60th |
| Vacant | Mar 4, 1909 – Mar 17, 1909 | | 61st | 21 | Re-elected in 1909. |
| 21 |  George T. Oliver | Republican | Mar 17, 1909 – Mar 3, 1917 | Elected to finish Knox's term |
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| Re-elected in 1911.Retired. | 22 | 62nd |
| 63rd |
| 64th | 22 | Re-elected in 1914. |
| 22 |  Philander C. Knox | Republican | Mar 4, 1917 – Oct 12, 1921 | Elected in 1916.Died. | 23 | 65th |
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| 66th |
| 67th | 23 | Re-elected in 1920.Died. |
| Vacant | Oct 12, 1921 – Oct 24, 1921 | |
| 23 |  William E. Crow | Republican | Oct 24, 1921 – Aug 2, 1922 | Appointed to continue Knox's term.Died. |
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| | Dec 31, 1921 – Jan 9, 1922 | Vacant |
| Appointed to continue Penrose's term.Elected to finish Penrose's term.Lost renomination. | Jan 9, 1922 – Mar 3, 1927 | Republican |  George W. Pepper | 18 |
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| Vacant | Aug 2, 1922 – Aug 8, 1922 | |
| 24 |  David A. Reed | Republican | Aug 8, 1922 – Jan 3, 1935 | Appointed to continue Knox's term.Elected to finish Knox's term. |
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| Elected in 1922. | 24 | 68th |
| 69th |
| 70th | 24 | William Scott Vare (R) waselected in 1926, but the Governor refused to certify the election and the Senate refused to qualify him. | Mar 4, 1927 – Dec 9, 1929 | Vacant |
| Re-elected in 1928.Lost re-election. | 25 | 71st |
| Appointed to continue Vare's term.Lost nomination to finish Vare's term. | Dec 11, 1929 – Dec 1, 1930 | Republican |  Joseph R. Grundy | 19 |
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| Elected in 1930 to finish Vare's term | Dec 2, 1930 – Jan 3, 1945 | Republican |  James J. Davis | 20 |
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| 72nd |
| 73rd | 25 | Re-elected in 1932. |
| 25 |  Joe Guffey | Democratic | Jan 3, 1935 – Jan 3, 1947 | Elected in 1934. | 26 | 74th |
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| 75th |
| 76th | 26 | Re-elected in 1938.Lost re-election. |
| Re-elected in 1940.Lost re-election. | 27 | 77th |
| 78th |
| 79th | 27 | Elected in 1944.Lost re-election. | Jan 3, 1945 – Jan 3, 1951 | Democratic |  Francis Myers | 21 |
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| 26 |  Edward Martin | Republican | Jan 3, 1947 – Jan 3, 1959 | Elected in 1946. | 28 | 80th |
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| 81st |
| 82nd | 28 | Elected in 1950.Lost re-election. | Jan 3, 1951 – Jan 3, 1957 | Republican |  James H. Duff | 22 |
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| Re-elected in 1952.Retired. | 29 | 83rd |
| 84th |
| 85th | 29 | Elected in 1956. | Jan 3, 1957 – Jan 3, 1969 | Democratic |  Joseph S. Clark Jr. | 23 |
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| 27 |  Hugh Scott | Republican | Jan 3, 1959 – Jan 3, 1977 | Elected in 1958. | 30 | 86th |
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| 87th |
| 88th | 30 | Re-elected in 1962.Lost re-election. |
| Re-elected in 1964. | 31 | 89th |
| 90th |
| 91st | 31 | Elected in 1968. | Jan 3, 1969 – Jan 3, 1981 | Republican |  Richard Schweiker | 24 |
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| Re-elected in 1970.Retired. | 32 | 92nd |
| 93rd |
| 94th | 32 | Re-elected in 1974.Retired. |
| 28 |  John Heinz | Republican | Jan 3, 1977 – Apr 4, 1991 | Elected in 1976. | 33 | 95th |
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| 96th |
| 97th | 33 | Elected in 1980. | Jan 3, 1981 – Jan 3, 2011 | Republican |  Arlen Specter | 25 |
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| Re-elected in 1982. | 34 | 98th |
| 99th |
| 100th | 34 | Re-elected in 1986. |
| Re-elected in 1988.Died. | 35 | 101st |
| 102nd |
| Vacant | Apr 4, 1991 – May 9, 1991 | |
| 29 |  Harris Wofford | Democratic | May 9, 1991 – Jan 3, 1995 | Appointed to continue Heinz's term.Elected to finish Heinz's term.Lost re-election. |
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| 103rd | 35 | Re-elected in 1992. |
| 30 |  Rick Santorum | Republican | Jan 3, 1995 – Jan 3, 2007 | Elected in 1994. | 36 | 104th |
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| 105th |
| 106th | 36 | Re-elected in 1998. |
| Re-elected in 2000.Lost re-election. | 37 | 107th |
| 108th |
| 109th | 37 | Re-elected in 2004.Changed party on Apr 28, 2009.Lost renomination. |
| 31 |  Bob Casey Jr. | Democratic | Jan 3, 2007 – Jan 3, 2025 | Elected in 2006. | 38 | 110th |
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| 111th |
| Democratic |
| 112th | 38 | Elected in 2010. | Jan 3, 2011 – Jan 3, 2023 | Republican |  Pat Toomey | 26 |
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| Re-elected in 2012. | 39 | 113th |
| 114th |
| 115th | 39 | Re-elected in 2016.Retired. |
| Re-elected in 2018.Lost re-election.[6] | 40 | 116th |
| 117th |
| 118th | 40 | Elected in 2022. | Jan 3, 2023 – present | Democratic |  John Fetterman | 27 |
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| 32 |  Dave McCormick | Republican | Jan 3, 2025 – present | Elected in 2024.[6] | 41 | 119th |
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| 120th |
| 121st | 41 | To be determined in the 2028 election. |
| To be determined in the 2030 election. | 42 | 122nd |
| # | Senator | Party | Years in office | Electoral history | T | C | T | Electoral history | Years in office | Party | Senator | # |
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| Class 1 | Class 3 |
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