• O'Brien, Dermod PRHA, HRA
• O'Brien, Geraldine
• Ó'Colmáin, Séamus
• O'Conchubhair, P
• O'Connor, Sean
• O'Donnell, Deirdre
• O'Halloran, James
• O'Hara, Helen
• O'Malley, Tony HRHA
• O'Neill, Ken
• O'Neill, Mark
• O'Ryan, Fergus RHA
• Olsson, Albert Julius
• Orlandi, Barbara
• Orpen, Sir William RA,RHA, RWS