| Professor Olsen FBA | Year of birth 1900 | Year of death 1900 | Year elected 1918 | Fellowship category Corresponding |
| Sir Charles Oman KBE, FBA | Year of birth 1860 | Year of death 1946 | Year elected 1905 | Fellowship category UK |
| Revd Dr John Wood Oman FBA | Year of birth 1860 | Year of death 1939 | Year elected 1938 | Fellowship category UK |
| M Henri Omont FBA | Year of birth 1857 | Year of death 1940 | Year elected 1914 | Fellowship category Corresponding |
| Dr Charles Onions CBE, FBA | Year of birth 1873 | Year of death 1965 | Year elected 1938 | Fellowship category UK |
| Mrs Iona Opie CBE, FBA | Year of birth 1923 | Year of death 2017 | Year elected 1998 | Fellowship category UK Emeritus |
| Mr Paul Oppé CB, FBA | Year of birth 1878 | Year of death 1957 | Year elected 1952 | Fellowship category UK |
| Professor Adolf Leo Oppenheim FBA | Year of birth 1904 | Year of death 1974 | Year elected 1971 | Fellowship category Corresponding |
| Professor Dr Anastasios K Orlandos FBA | Year of birth 1887 | Year of death 1979 | Year elected 1971 | Fellowship category Corresponding |
| Professor John Orr FBA | Year of birth 1885 | Year of death 1966 | Year elected 1952 | Fellowship category UK |
| Professor George Ostrogorsky FBA | Year of birth 1902 | Year of death 1976 | Year elected 1963 | Fellowship category Corresponding |
| Professor Elinor Ostrom NULL | Year of birth 1933 | Year of death 2012 | Year elected 2012 | Fellowship category Corresponding |
| Professor Dr Heinrich Otten FBA | Year of birth 1913 | Year of death 2012 | Year elected 1991 | Fellowship category Corresponding |
| Professor Walter Otto FBA | Year of birth 1900 | Year of death 1900 | Year elected 1938 | Fellowship category Corresponding |
| Professor Gwilym Owen FBA | Year of birth 1922 | Year of death 1982 | Year elected 1969 | Fellowship category UK |
| Professor Dr Tahsin Ozguc FBA | Year of birth 1900 | Year of death 2005 | Year elected 1969 | Fellowship category Corresponding |