- O'Brien, Abigail
- O'Brien, Dermod
- O'Brien, Edna
- O'Brien, Geraldine
- O'Brien, Gretta
- O'Brien, Kieran Doyle
- O'Brien, Kitty Wilmer
- O'Brien, Louise
- O'Brien, Susan
- O'Byrne, Vincent
- O'Casey, Breon
- O'Casey, Sean
- O'Ciobhain, Blaithin
- O'Colmain, Seamus
- O'Connell, Beatrice
- O'Connell, Eilis
- O'Connell, John
- O'Connell, Lesley Ann
- O'Connor, Carol
- O'Connor, Frank
- O'Connor, James
- O'Connor, James Arthur
- O'Connor, Joseph
- O'Connor, Sean
- O'Conor, Roderic
- O'Dea, Mick
- O'Doherty, Eamonn
- O'Donnell, Deirdre
- O'Donnell, Ruth
- O'Donnell, Simon
- O'Donoghue, Hughie
- O'Dowd, Gwen
- O'Faolain, Sean
- O'Flaherty, Dervla
- O'Flatherty, Killian
- O'Gara, Aine
- O'Hagan, Harriet Osborne
- O'Halloran, Robbie
- O'Higgins, Helen
- O'Kane, David
- O'Kane, Eamon
- O'Kelly, Aloysius
- O'Kelly, Mark
- O'Leary, Cormac
- O'Leary, John
- O'Loughlin, Cally
- O'Malley, Jane
- O'Malley, Tony
- O'Neill, Alannah
- O'Neill, Daniel
- O'Neill, Gay
- O'Neill, Geraldine
- O'Neill, Liam
- O'Neill, Mark
- O'Neill, Mary Rose
- O'Neill, Michael
- O'Neill, Richard
- O'Neill, William
- O'Neill-Gallagher, F
- O'Neill-Laher, Mairead
- O'Nolan, James
- O'Reilly, John
- O'Reilly, Patrick
- O'Reilly, T.
- O'Ryan, Fergus
- O'Suilleabhain, Fiachra
- O'Sullivan, Donal
- O'Sullivan, Margaret
- O'Sullivan, Patrick
- O'Sullivan, Sean
- Oakley, George
- Ofen, Michael van
- Olsson, Julius PPRA
- OMANN, GUNNI
- Omersa, Dimitri
- Orpen, Bea
- Orpen, Sir William
- Osborne, Dennis
- Osborne, Sir Walter Frederick
- Osborne, William
- Osbourne, John
