List of former members of the United States House of Representatives (O) Number of years/terms representative/delegate has served Number of years/terms representative/delegate has served

| Representative | Years | State_ | Party | Lifespan |
|---|---|---|---|---|
| Frank T. O`Hair | 1913–1915 | Illinois | Democratic | 1870–1932 |
| 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 |
| Alvin O`Konski | 1943–1973 | Wisconsin | Republican | 1904–1987 |
| Denis O`Leary | 1913–1914 | New York | Democratic | 1863–1943 |
| James A. O`Leary | 1935–1944 | New York | Democratic | 1889–1944 |
| 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 |