| O'Hare, Denis | Denis O'Hare | Actor | 1984 | 1 | |
| O'Hare, Tim | Tim O'Hare | Designer | 2004 | 1 | |
| O'Hea, Brendan | Brendan O'Hea | Actor | 1993 - 1999 | 6 | 1 |
| O'Hearn, Susan, P. | Susan P. O'Hearn | Director | 2018 | 1 | |
| O'Horn, Nigel | Nigel O'Horn | Adaptation | 2017 | 1 | |
| O'Kane, John | John O'Kane | Actor | 2021 | 1 | |
| O'Kane, Nancy | Nancy O'Kane | Actor | 1952 - 1961 | 2 | |
| O'Kane, Owen | Owen O'Kane | Actor | 2003 | 1 | |
| O'Kane, Patrick | Patrick O'Kane | Actor | 2000 | 1 | 1 |
| O'Keefe, Joseph | Joseph O'Keefe | Actor | 2001 | 1 | |
| O'Keefe, Nathan | Nathan O'Keefe | Actor | 2008 - 2017 | 3 | |
| O'Keefe, Nina | Nina O'Keefe | Actor | 2011 | 1 | |
| O'Keefe, Tim | Tim O'Keefe | Actor | 2012 | 2 | |
| O'Keeffe, Lorraine | Lorraine O'Keeffe | Actor | 1993 | 1 | |
| O'Kelly, Aideen | Aideen O'Kelly | Actor | 1985 | 1 | |
| O'Kelly, Geri | Geri O'Kelly | Choreographer | 1993 | 1 | |
| O'Leary, Bridget Kathleen | Bridget Kathleen O'Leary | Director | 2011 | 1 | |
| O'Leary, Harold | Harold O'Leary | Actor | 2003 | 1 | |
| O'Leary, Muriel | Muriel O'Leary | Actor | 1940 | 1 | |
| O'Leary, Pascal | Pascal O'Leary | Director | 2024 | 1 | |
| O'Leary, Ursula | Ursula O'Leary | Actor | 1950 | 1 | |
| O'Lochlainn, Gearoid | Gearoid O'Lochlainn | Actor, Translator | 1928 - 2009 | 2 | |
| O'Lochlinn, Sheila | Sheila O'Lochlinn | Actor | 1936 | 1 | |
| O'Mahoney, Robert | Robert O'Mahoney | Actor, Author | 1982 - 1991 | 10 | |
| O'Mahony, Paul | Paul O'Mahony | Designer | 2013 - 2017 | 3 | |
| O'Malley, Cathleen | Cathleen O'Malley | Assistant Director | 2022 | 1 | |
| O'Malley, Flynn | Flynn O'Malley | Actor | 1963 | 1 | |
| O'Malley, Geraldine | Geraldine O'Malley | Costume Designer, Designer | 1989 - 1990 | 4 | |
| O'Malley, Tom | Tom O'Malley | Actor | 1949 | 4 | |
| O'Mara, Kate | Kate O'Mara | Actor | 1981 | 1 | |
| O'Mara, Mollie | Mollie O'Mara | Actor | 1993 | 1 | |
| O'Neal, Timothy | Timothy O'Neal | Actor | 2006 | 1 | |
| O'Neil, Barry | Barry O'Neil | Director | 1909 | 1 | |
| O'Neil, Nance | Nance O'Neil | Actor | 1900 - 1917 | 23 | 1 |
| O'Neil, Randall | Randall O'Neil | Designer | 1948 | 1 | |
| O'Neil, Raymond | Raymond O'Neil | Actor | 2000 | 1 | |
| O'Neil, Rebecca Pugh Parker | Rebecca Pugh Parker O'Neil | Actor | 2023 | 1 | |
| O'Neil, Sally | Sally O'Neil | Actor | 1939 | 1 | |
| O'Neil, Ted | Ted O'Neil | Actor | 2009 | 1 | |
| O'Neill, Aron, Arnarson | Aron Arnarson O'Neill | Actor | 2012 | 1 | |
| O'Neill, Chris | Chris O'Neill | Designer, Lighting Designer | 2011 | 2 | |
| O'Neill, Daniel | Daniel O'Neill | Actor | 2013 | 1 | |
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