# List of former members of the United States House of Representatives (O)

This is a complete list of former members of the United States House of Representatives whose last names begin with the letter O.

## Number of years/terms representative/delegate has served

The number of years the representative/delegate has served in Congress indicates the number of terms the representative/delegate has. Note the representative/delegate can also serve non-consecutive terms if the representative/delegate loses election and wins re-election to the House.
* 2 years - 1 or 2 terms
* 4 years - 2 or 3 terms
* 6 years - 3 or 4 terms
* 8 years - 4 or 5 terms
* 10 years - 5 or 6 terms
* 12 years - 6 or 7 terms
* 14 years - 7 or 8 terms
* 16 years - 8 or 9 terms
* 18 years - 9 or 10 terms
* 20 years - 10 or 11 terms
* 22 years - 11 or 12 terms
* 24 years - 12 or 13 terms
* 26 years - 13 or 14 terms
* 28 years - 14 or 15 terms
* 30 years - 15 or 16 terms
* 32 years - 16 or 17 terms
* 34 years - 17 or 18 terms
* 36 years - 18 or 19 terms
* 38 years - 19 or 20 terms
* 40 years - 20 or 21 terms
* 42 years - 21 or 22 terms
* 44 years - 22 or 23 terms
* 46 years - 23 or 24 terms
* 48 years - 24 or 25 terms
* 50 years - 25 or 26 terms
* 52 years - 26 or 27 terms
* 54 years - 27 or 28 terms
* 56 years - 28 or 29 terms
* 58 years - 29 or 30 terms
| Representative/Delegate | Years | State/Territory | Party | Lifespan |
| Mary Rose Oakar | 1977–1993 | Ohio | Democratic | 1940–present |
| P. Davis Oakey | 1915–1917 | Connecticut | Republican | 1861–1920 |
| Thomas Jackson Oakley | 1813–1815 | New York | Federalist | 1783–1857 |
| Thomas Jackson Oakley | 1827–1828 | New York | Democratic | 1783–1857 |
| Charles G. Oakman | 1953–1955 | Michigan | Republican | 1903–1973 |
| William C. Oates | 1881–1894 | Alabama | Democratic | 1835–1910 |
| Jim Oberstar | 1975–2011 | Minnesota | Democratic-Farmer-Labor | 1934–2014 |
| Dave Obey | 1969–2011 | Wisconsin | Democratic | 1938–present |
| Charles F.X. O'Brien | 1921–1925 | New Jersey | Democratic | 1879–1940 |
| George D. O'Brien | 1937–1939 1941–1947 1949–1955 | Michigan | Democratic | 1900–1957 |
| George M. O'Brien | 1973–1986 | Illinois | Republican | 1917–1986 |
| James O'Brien | 1879–1881 | New York | Independent Democrat | 1841–1907 |
| James H. O'Brien | 1913–1915 | New York | Democratic | 1860–1924 |
| Jeremiah O'Brien | 1823–1825 | Maine | Democratic-Republican | 1778–1858 |
| Jeremiah O'Brien | 1825–1829 | Maine | National Republican | 1778–1858 |
| Joseph J. O'Brien | 1939–1945 | New York | Republican | 1897–1953 |
| Leo W. O'Brien | 1952–1966 | New York | Democratic | 1900–1982 |
| Thomas J. O'Brien | 1933–1939 1943–1964 | Illinois | Democratic | 1878–1964 |
| William J. O'Brien | 1873–1877 | Maryland | Democratic | 1836–1905 |
| William S. O'Brien | 1927–1929 | West Virginia | Democratic | 1862–1948 |
| Pablo Ocampo | 1907–1909 | Philippines | None | 1853-1925 |
| Thomas P. Ochiltree | 1883–1885 | Texas | Independent | 1837–1902 |
| David J. O'Connell | 1919–1921 1923–1930 | New York | Democratic | 1868–1930 |
| Jeremiah E. O'Connell | 1923–1927 1929–1930 | Rhode Island | Democratic | 1883–1964 |
| Jerry J. O'Connell | 1937–1939 | Montana | Democratic | 1909–1956 |
| John Matthew O'Connell | 1933–1939 | Rhode Island | Democratic | 1872–1941 |
| Joseph F. O'Connell | 1907–1911 | Massachusetts | Democratic | 1872–1942 |
| Charles O'Connor | 1929–1931 | Oklahoma | Republican | 1878–1940 |
| James O'Connor | 1919–1931 | Louisiana | Democratic | 1870–1941 |
| James F. O'Connor | 1937–1945 | Montana | Democratic | 1878–1945 |
| John J. O'Connor | 1923–1939 | New York | Democratic | 1885–1960 |
| Michael P. O'Connor | 1879–1881 | South Carolina | Democratic | 1831–1881 |
| Caroline O'Day | 1935–1943 | New York | Democratic | 1875–1943 |
| Benjamin Barker Odell Jr. | 1895–1899 | New York | Republican | 1854–1926 |
| Moses F. Odell | 1861–1865 | New York | Democratic | 1818–1866 |
| N. Holmes Odell | 1875–1877 | New York | Democratic | 1828–1904 |
| James O'Donnell | 1885–1893 | Michigan | Republican | 1840–1915 |
| Charles T. O'Ferrall | 1884–1893 | Virginia | Democratic | 1840–1905 |
| Charles F. Ogden | 1919–1923 | Kentucky | Republican | 1873–1933 |
| David A. Ogden | 1817–1819 | New York | Federalist | 1770–1829 |
| Henry W. Ogden | 1894–1899 | Louisiana | Democratic | 1842–1905 |
| Alexander Ogle | 1817–1819 | Pennsylvania | Democratic-Republican | 1766–1832 |
| Andrew Jackson Ogle | 1849–1851 | Pennsylvania | Whig | 1822–1852 |
| Charles Ogle | 1837–1841 | Pennsylvania | Anti-Masonic | 1798–1841 |
| Charles Ogle | 1841 | Pennsylvania | Whig | 1798–1841 |
| Woodson R. Oglesby | 1913–1917 | New York | Democratic | 1867–1955 |
| James M. E. O'Grady | 1899–1901 | New York | Republican | 1863–1928 |
| Frank T. O'Hair | 1913–1915 | Illinois | Democratic | 1870–1932 |
| Tom O'Halleran | 2017–2023 | Arizona | Democratic | 1946–present |
| Barratt O'Hara | 1949–1951 1953–1969 | Illinois | Democratic | 1882–1969 |
| James E. O'Hara | 1883–1887 | North Carolina | Republican | 1844–1905 |
| James G. O'Hara | 1959–1977 | Michigan | Democratic | 1925–1989 |
| Joseph P. O'Hara | 1941–1959 | Minnesota | Republican | 1895–1975 |
| Lewis P. Ohliger | 1892–1893 | Ohio | Democratic | 1843–1923 |
| Alvin O'Konski | 1943–1973 | Wisconsin | Republican | 1904–1987 |
| J. Van Vechten Olcott | 1905–1911 | New York | Republican | 1856–1940 |
| Pearl Peden Oldfield | 1929–1931 | Arkansas | Democratic | 1876–1962 |
| William Allan Oldfield | 1909–1928 | Arkansas | Democratic | 1874–1928 |
| Edson B. Olds | 1849–1855 | Ohio | Democratic | 1802–1869 |
| Denis O'Leary | 1913–1914 | New York | Democratic | 1863–1943 |
| James A. O'Leary | 1935–1944 | New York | Democratic | 1889–1944 |
| Abram B. Olin | 1857–1863 | New York | Republican | 1808–1879 |
| Gideon Olin | 1803–1807 | Vermont | Democratic-Republican | 1743–1823 |
| Henry Olin | 1824–1825 | Vermont | National Republican | 1768–1837 |
| Jim Olin | 1983–1993 | Virginia | Democratic | 1920–2006 |
| Andrew Oliver | 1853–1857 | New York | Democratic | 1815–1889 |
| Daniel C. Oliver | 1917–1919 | New York | Democratic | 1865–1924 |
| Frank A. Oliver | 1923–1934 | New York | Democratic | 1883–1968 |
| James C. Oliver | 1937–1943 | Maine | Republican | 1895–1986 |
| James C. Oliver | 1959–1961 | Maine | Democratic | 1895–1986 |
| Mordecai Oliver | 1853–1855 | Missouri | Whig | 1819–1898 |
| Mordecai Oliver | 1855–1857 | Missouri | Oppositionist | 1819–1898 |
| S. Addison Oliver | 1875–1879 | Iowa | Republican | 1833–1912 |
| William Bacon Oliver | 1915–1937 | Alabama | Democratic | 1867–1948 |
| William M. Oliver | 1841–1843 | New York | Democratic | 1792–1863 |
| Marlin Edgar Olmsted | 1897–1913 | Pennsylvania | Republican | 1847–1913 |
| Richard Olney II | 1915–1921 | Massachusetts | Democratic | 1871–1939 |
| Kathryn O'Loughlin McCarthy | 1933–1935 | Kansas | Democratic | 1894-1952 |
| Archibald E. Olpp | 1921–1923 | New Jersey | Republican | 1882–1949 |
| Arnold Olsen | 1961–1971 | Montana | Democratic | 1916–1990 |
| Alec G. Olson | 1963–1967 | Minnesota | Democratic-Farmer-Labor | 1930–present |
| Pete Olson | 2009–2021 | Texas | Republican | 1962–present |
| John Olver | 1991–2013 | Massachusetts | Democratic | 1936–2023 |
| Matthew Vincent O'Malley | 1931 | New York | Democratic | 1878–1931 |
| Thomas O'Malley | 1933–1939 | Wisconsin | Democratic | 1903–1979 |
| Emmet O'Neal | 1935–1947 | Kentucky | Democratic | 1887–1967 |
| Maston E. O'Neal Jr. | 1965–1971 | Georgia | Democratic | 1907–1990 |
| John H. O'Neall | 1887–1891 | Indiana | Democratic | 1838–1907 |
| Joseph H. O'Neil | 1889–1895 | Massachusetts | Democratic | 1853–1935 |
| Charles O'Neill | 1863–1871 1873–1893 | Pennsylvania | Republican | 1821–1893 |
| Edward L. O'Neill | 1937–1939 | New Jersey | Democratic | 1903–1948 |
| Harry P. O'Neill | 1949–1953 | Pennsylvania | Democratic | 1889–1953 |
| John O'Neill | 1863–1865 | Ohio | Democratic | 1822–1905 |
| John Joseph O'Neill | 1883–1889 1891–1893 1894–1895 | Missouri | Democratic | 1846–1898 |
| Tip O'Neill | 1953–1987 | Massachusetts | Democratic | 1912–1994 |
| Daniel O'Reilly | 1879–1881 | New York | Independent Democrat | 1838–1911 |
| Stephen Ormsby | 1811–1813 1813–1817 | Kentucky | Democratic-Republican | 1759–1844 |
| Beto O'Rourke | 2013–2019 | Texas | Democratic | 1972–present |
| Alexander D. Orr | 1792–1795 | Kentucky | Anti-Administration | 1761–1835 |
| Alexander D. Orr | 1795–1797 | Kentucky | Democratic-Republican | 1761–1835 |
| Benjamin Orr | 1817–1819 | Massachusetts | Federalist | 1772–1828 |
| Jackson Orr | 1871–1875 | Iowa | Republican | 1832–1926 |
| James Lawrence Orr | 1849–1859 | South Carolina | Democratic | 1822–1873 |
| Robert Orr Jr. | 1825–1829 | Pennsylvania | Democratic | 1786–1876 |
| Godlove Stein Orth | 1863–1871 1873–1875 1879–1882 | Indiana | Republican | 1817–1882 |
| Solomon Ortiz | 1983–2011 | Texas | Democratic | 1937–present |
| Bill Orton | 1991–1997 | Utah | Democratic | 1948–2009 |
| Edwin Sylvanus Osborne | 1885–1891 | Pennsylvania | Republican | 1839–1900 |
| Henry Z. Osborne | 1917–1923 | California | Republican | 1848–1923 |
| John Eugene Osborne | 1897–1899 | Wyoming | Democratic | 1858–1943 |
| Thomas Burr Osborne | 1839–1843 | Connecticut | Whig | 1798–1869 |
| Tom Osborne | 2001–2007 | Nebraska | Republican | 1937–present |
| Doug Ose | 1999–2005 | California | Republican | 1955–present |
| Gayton P. Osgood | 1833–1835 | Massachusetts | Democratic | 1797–1861 |
| George F. O'Shaunessy | 1911–1919 | Rhode Island | Democratic | 1868–1934 |
| Camilo Osías | 1929–1935 | Philippines | None | 1889–1976 |
| James H. Osmer | 1879–1881 | Pennsylvania | Republican | 1832–1912 |
| Frank C. Osmers Jr. | 1939–1943 1951–1965 | New Jersey | Republican | 1907–1977 |
| Harold C. Ostertag | 1951–1965 | New York | Republican | 1896–1985 |
| Eugene D. O'Sullivan | 1949–1951 | Nebraska | Democratic | 1883–1968 |
| Patrick B. O'Sullivan | 1923–1925 | Connecticut | Democratic | 1887–1978 |
| Mariano S. Otero | 1879–1881 | New Mexico | Republican | 1844-1904 |
| Miguel Antonio Otero | 1856–1861 | New Mexico | Democratic | 1829-1882 |
| Peter J. Otey | 1895–1902 | Virginia | Democratic | 1840–1902 |
| Harrison Gray Otis | 1797–1801 | Massachusetts | Federalist | 1765–1848 |
| John Otis | 1849–1851 | Maine | Whig | 1801–1856 |
| John G. Otis | 1891–1893 | Kansas | Populist | 1838–1916 |
| Norton P. Otis | 1903–1905 | New York | Republican | 1840–1905 |
| Theobald Otjen | 1895–1907 | Wisconsin | Republican | 1851–1924 |
| Donald L. O'Toole | 1937–1953 | New York | Democratic | 1902–1964 |
| Butch Otter | 2001–2007 | Idaho | Republican | 1942–present |
| Richard Ottinger | 1965–1971 1975–1985 | New York | Democratic | 1929–present |
| Granville H. Oury | 1881–1885 | Arizona | Democratic | 1825-1891 |
| Joseph H. Outhwaite | 1885–1895 | Ohio | Democratic | 1841–1907 |
| George E. Outland | 1943–1947 | California | Democratic | 1906–1981 |
| David Outlaw | 1847–1853 | North Carolina | Whig | 1806–1868 |
| George Outlaw | 1825 | North Carolina | Democratic-Republican | 1771–1825 |
| Arthur W. Overmyer | 1915–1919 | Ohio | Democratic | 1879–1952 |
| James Overstreet | 1819–1822 | South Carolina | Democratic-Republican | 1773–1822 |
| James W. Overstreet | 1906–1907 1917–1923 | Georgia | Democratic | 1866–1938 |
| Jesse Overstreet | 1895–1909 | Indiana | Republican | 1859–1910 |
| Edward Overton Jr. | 1877–1881 | Pennsylvania | Republican | 1836–1903 |
| John H. Overton | 1931–1933 | Louisiana | Democratic | 1875–1948 |
| Walter Hampden Overton | 1829–1831 | Louisiana | Democratic | 1788–1845 |
| Allen Ferdinand Owen | 1849–1851 | Georgia | Whig | 1816–1865 |
| Emmett Marshall Owen | 1933–1939 | Georgia | Democratic | 1877–1939 |
| George Washington Owen | 1823–1825 | Alabama | Democratic-Republican | 1796–1837 |
| George Washington Owen | 1825–1829 | Alabama | Democratic | 1796–1837 |
| James Owen | 1817–1819 | North Carolina | Democratic-Republican | 1784–1865 |
| Robert Dale Owen | 1843–1847 | Indiana | Democratic | 1801–1877 |
| Ruth Bryan Owen | 1929–1933 | Florida | Democratic | 1885–1954 |
| William D. Owen | 1885–1891 | Indiana | Republican | 1846–19?? |
| Bill Owens | 2009–2015 | New York | Democratic | 1949–present |
| George Welshman Owens | 1835–1839 | Georgia | Democratic | 1786–1856 |
| James W. Owens | 1889–1893 | Ohio | Democratic | 1837–1900 |
| Major Owens | 1983–2007 | New York | Democratic | 1936–2013 |
| Thomas L. Owens | 1947–1948 | Illinois | Republican | 1897–1948 |
| Wayne Owens | 1973–1975 1987–1993 | Utah | Democratic | 1937–2002 |
| William Claiborne Owens | 1895–1896 | Kentucky | Democratic | 1849–1925 |
| William Claiborne Owens | 1896–1897 | Kentucky | Republican | 1849–1925 |
| Bryan Owsley | 1841–1843 | Kentucky | Whig | 1798–1849 |
| Mike Oxley | 1981–2007 | Ohio | Republican | 1944–2016 |