Alphabetical List
- Harold Callahan Oatway
- Charles Gordon O'Brien
- Edward William O'Brien
- George Allan O'Brien
- Henry James Stuart O'Brien
- John Joseph O'Brien
- William Lawrence Stuart O'Brien
- Brian Patrick Barry O'Callaghan
- Robert Hay Lismore O'Callaghan
- Carroll Alexander Odell
- James Leonard O'Donnell
- Douglas Albert Ogilvie
- Douglas Rolt Ogilvie
- Ian J. Ogilvie
- James Deuchars Boyd Ogilvie
- Robert N. Ogilvie
- James Howard Wainwright O'Gorman
- F. Victor Ogulnik
- Dennis O'Donnell O'Higgins
- Edward Andrew O'Neill O'Higgins
- Michael Brian O'Leary
- Abraham Oliver
- Austen William Oliver
- Howard Thomas Oliver
- Jean Catherine Oliver
- Michael Kelway Oliver
- Louis Charles Olker
- Frank S. Olmes
- Shirley Herbert Olmstead
- Kaare Olsen
- Rolph (or Rolf) Olsen
- Michael J. O'Mara
- Robert Stewart O'Meara
- Robert Stuart O'Neil
- Vincent D. O'Neil
- Edward Yates O'Neill
- Gordon Campbell O'Neill
- Melville Henderson O'Neill
- Stuart Richard Oney
- John Edward Openshaw
- James Stephen Oppe
- John Stephen Oppe
- Louis Orbane
- James Meredith O'Reilly
- Frederick Thomas O'Reilly-Hewitt
- John Kenneth Tweedale Ormrod
- William Ornstein
- Edward deLery Orr
- John Cecil Orr
- Robert Rice Orr
- William Leonard Orr
- F. Fitz Osborne
- John R. Osborne
- John Somerset Osborne
- Philip Featherstone Osler
- Thomas Richard Osler
- Paul M. Osmun
- Peter Andrew Ostapovitch
- Pierre Emile Ostiguy
- William Edward Douglas Oswald
- Angus Winn Oughtred
- William Wallace Oughtred
- Paul Alderic Ouimet
- Paul J. Ouimet
- Leslie Frank Ounsworth
- Murray MacLaren Outhet
- Damaris Enid Hendrie Owen
- Francis James Owen
- Frank Herbert Owen
- George Owen
- Herbert Frank Owen
- Hugh Glyn Owen
- Jean Nancy Owen
- Andrew Paul Owens
- Owen Ernest Owens
- Bernard Anderson Ower
