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 |
|---|---|---|---|---|
| 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 |