- John Wright Oakes
- Agnes Oakley
- Octavius Oakley
- Philip Oakley
- James George Oben
- James Arthur O’Connor
- John O’Connor
- Francis Joseph O’Donohoe
- John Offley
- Henry Alexander Ogg
- Frank Stanley Ogilvie
- Frederick Dove Ogilvie
- Jane Mary Oglander
- John Connel Ogle
- Helen O’Hara
- John O’Keeffe
- John Edwin Oldfield
- G. R. Oldham
- J. C. Oldmeadow
- John Oliphant
- Emma Sophia Oliver
- Herbert Arnold Oliver
- William Oliver
- Frank O’Meara
- Rowland Omer
- Henry O’Neill
- Henry Nelson O’Neill
- Hugh O’Neill
- Edward Oram
- William Oram
- Montague Frederick O’Reilly
- Daniel Orme
- Edward Orme
- William Orme
- George Ormerod
- James Orrock
- Walter Frederick Osborne
- Samuel William Oscroft
- Henry Ospovat
- John H. Oswald
- Charles Bethell Otley
- Benjamin John Ottewell
- Emily Ottley
- William Young Ottley
- Philip John Ouless YP
- William Gore Ouselry
- William Heysham Overend
- Edward Pryce Owen
- Samuel Owen
- George Oyston
