| Yemi Osinbajo | 14th Vice President of Nigeria | 1957 |
| Frank Oski | American pediatrician | 1932–1996 |
| William Osler | Canadian pathologist, physici… | 1849–1919 |
| Liban Yusuf Osman | Politician | |
| Emily Osment | American actress | 1992 |
| Laura Osnes | actress | 1985 |
| Jon Ossoff | American politician | 1987 |
| Joel Osteen | American televangelist and au… | 1963 |
| Alexander Osterwalder | Austrian business theorist | 1974 |
| Osthanes | pen-name used by several pseu… | -500 |
| Elinor Ostrom | American political economist | 1933–2012 |
| Vincent Ostrom | American academic, educator a… | 1919–2012 |
| Gilbert O'Sullivan | Irish singer-songwriter | 1946 |
| Alice Oswald | British poet | 1966 |
| Patton Oswalt | stand-up comedian | 1969 |
| Paul Otellini | former president & CEO of Int… | 1950–2017 |
| Carré Otis | American actress and model | 1968 |
| Peter O'Toole | Irish film and stage actor | 1932–2013 |
| Julie Otsuka | writer | 1962 |
| Roza Otunbayeva | Soviet diplomat | 1950 |
| Thomas Otway | English writer | 1652–1685 |
| Francisco Ou | Taiwanese politician | 1940 |
| Ouida | British novelist | 1839–1908 |
| P. D. Ouspensky | Russian esotericist | 1878–1947 |
| Moni Ovadia | Italian actor, musician, sing… | 1946 |
| Nicholas Ovcharov | Ukrainian writer and film dir… | 1988 |
| Alexander Ovechkin | Russian ice hockey player | 1985 |
| Thomas Overbury | (1581–1613) English poet and… | 1581–1613 |
| Dennis Overbye | American writer | 1944 |
| Richard Overy | British historian | 1947 |
| Ovid | Roman poet | -43–17 BC |
| Owain Owain | Welsh novelist, short story w… | 1929–1993 |
| Asaduddin Owaisi | Indian politician | 1969 |
| James A. Owen | Illustrator | 1969 |
| John Owen | English theologian | 1616–1683 |
| Richard Owen | English biologist | 1804–1892 |
| Robert Owen | Welsh social reformer | 1771–1858 |
| Wilfred Owen | English poet and soldier (189… | 1893–1918 |
| Buck Owens | American country singer-songw… | 1929–2006 |
| Jesse Owens | American track and field athl… | 1913–1980 |
| Montell Owens | American football player, run… | 1984 |
| Terrell Owens | former American football wide… | 1973 |
| Derek Owusu | | |
| Edward de Vere, 17th Earl of Oxford | English peer and courtier of … | 1550–1604 |
| David W. Oxtoby | President of Pomona college | 1951 |
| Adenike Oyetunde | Nigerian founder of amputees … | 1986 |
| Helen Oyeyemi | British author | 1984 |
| Amos Oz | Israeli writer, novelist, jou… | 1939–2018 |
| Kaori Ozaki | Japanese mangaka | 1976 |
| Jacques Ozanam | French mathematician | 1640–1718 |
| Ruth Ozeki | American writer | 1956 |
| Cynthia Ozick | American writer | 1928 |
| Ray Ozzie | American businessman | 1955 |
