| O'Mahony, Paul | Paul O'Mahony | Designer | 2013 - 2017 | 3 | |
| O'Mahoney, Robert | Robert O'Mahoney | Actor, Author | 1982 - 1991 | 10 | |
| O'Lochlinn, Sheila | Sheila O'Lochlinn | Actor | 1936 | 1 | |
| O'Lochlainn, Gearoid | Gearoid O'Lochlainn | Actor, Translator | 1928 - 2009 | 2 | |
| O'Leary, Ursula | Ursula O'Leary | Actor | 1950 | 1 | |
| O'Leary, Pascal | Pascal O'Leary | Director | 2024 | 1 | |
| O'Leary, Muriel | Muriel O'Leary | Actor | 1940 | 1 | |
| O'Leary, Harold | Harold O'Leary | Actor | 2003 | 1 | |
| O'Leary, Bridget Kathleen | Bridget Kathleen O'Leary | Director | 2011 | 1 | |
| O'Kelly, Geri | Geri O'Kelly | Choreographer | 1993 | 1 | |
| O'Kelly, Aideen | Aideen O'Kelly | Actor | 1985 | 1 | |
| O'Keeffe, Lorraine | Lorraine O'Keeffe | Actor | 1993 | 1 | |
| O'Keefe, Tim | Tim O'Keefe | Actor | 2012 | 2 | |
| O'Keefe, Nina | Nina O'Keefe | Actor | 2011 | 1 | |
| O'Keefe, Nathan | Nathan O'Keefe | Actor | 2008 - 2017 | 3 | |
| O'Keefe, Joseph | Joseph O'Keefe | Actor | 2001 | 1 | |
| O'Kane, Patrick | Patrick O'Kane | Actor | 2000 | 1 | 1 |
| O'Kane, Owen | Owen O'Kane | Actor | 2003 | 1 | |
| O'Kane, Nancy | Nancy O'Kane | Actor | 1952 - 1961 | 2 | |
| O'Kane, John | John O'Kane | Actor | 2021 | 1 | |
| O'Horn, Nigel | Nigel O'Horn | Adaptation | 2017 | 1 | |
| O'Hearn, Susan, P. | Susan P. O'Hearn | Director | 2018 | 1 | |
| O'Hea, Brendan | Brendan O'Hea | Actor | 1993 - 1999 | 6 | 1 |
| O'Hare, Tim | Tim O'Hare | Designer | 2004 | 1 | |
| O'Hare, Denis | Denis O'Hare | Actor | 1984 | 1 | |
| O'Hare, Damian | Damian O'Hare | Actor | 2003 | 1 | |
| O'Hara, Lesley | Lesley O'Hara | Actor | 1972 | 1 | |
| O'Hara, John, Ryker | John Ryker O'Hara | Actor | 1985 | 2 | |
| O'Hara, Jill | Jill O'Hara | Actor | 1971 | 1 | 1 |
| O'Hara, Caitlin | Caitlin O'Hara | Designer | 2013 | 1 | |
| O'Hara, Audrey | Audrey O'Hara | Actor | 1956 | 1 | |
| O'Hanlon, Shelagh | Shelagh O'Hanlon | Actor | 1951 | 1 | |
| O'Hanlon, Máire | Máire O'Hanlon | Actor | 1980 | 16 | |
| O'Grady, Sorcha | Sorcha O'Grady | Actor | 2011 | 1 | |
| O'Grady, Frank | Frank O'Grady | Actor | 1932 | 1 | |
| O'Grady, Chris | Chris O'Grady | Actor | 2011 | 1 | |
| O'Gara, Penn | Penn O'Gara | Costume Designer | 2019 | 1 | |
| O'Gara, Patrick | Patrick O'Gara | Actor | 1973 | 1 | |
| O'Foghludha, Michael | Michael O'Foghludha | Actor | 2001 | 1 | |
| O'Flyn, Audrey | Audrey O'Flyn | Actor | 1936 | 2 | |
| O'Flanagan, Lucille | Lucille O'Flanagan | Actor | 1985 | 1 | |
| O'Flaherty, Michael | Michael O'Flaherty | Musical Director | 1984 | 1 | |
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