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.

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
1827–1828 Democratic
Charles G. Oakman 1953–1955 Michigan Republican 1903–1973
William C. Oates 1881–1894 Alabama Democratic 1835–1910
James 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
1825–1829 National Republican
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
1841 Whig
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
1959–1961 Democratic
Mordecai Oliver 1853–1855 Missouri Whig 1819–1898
1855–1857 Oppositionist
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
1795–1797 Democratic-Republican
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
1825–1829 Democratic
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
1896–1897 Republican
Bryan Owsley 1841–1843 Kentucky Whig 1798–1849
Mike Oxley 1981–2007 Ohio Republican 1944–2016

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