Following is an incomplete list of past and present Members of Parliament (MPs) of the United Kingdom whose surnames begin with O. The dates in parentheses are the periods for which they were MPs.
Francis O'Beirne Sir Bill O'Brien (1983–2005) Cornelius O'Brien Sir Edward O'Brien, 4th Baronet J. F. X. O'Brien James O'Brien John O'Brien Lucius O'Brien, 13th Baron Inchiquin Mike O'Brien (1992–2010) Patrick O'Brien Stephen O'Brien (1999–2015) William O'Brien William Smith O'Brien Charles O'Connell Daniel O'Connell Daniel O'Connell Jnr John O'Connell Maurice O'Connell Art O'Connor Arthur O'Connor Feargus O'Connor John O'Connor John O'Connor Morgan John O'Connell T. P. O'Connor (1880–1929) James Edward O'Doherty Joseph O'Doherty Philip O'Doherty William O'Doherty Charles James O'Donnell (1906–1910) John O'Donnell Frank Hugh O'Donnell Thomas O'Donnell Daniel O'Donoghue Anthony O'Flaherty Patrick O'Keeffe Conor O'Kelly John J. O'Kelly Seán T. O'Kelly Thomas O'Hagan, 1st Baron O'Hagan Thomas O'Hanlon Edward O'Hara (1990–2010) Patrick O'Hea Brian O'Higgins Pádraic Ó Máille Seán O'Mahony William O'Malley James O'Mara Arthur O'Neill Charles O'Neill Edward O'Neill, 2nd Baron O'Neill Hugh O'Neill, 1st Baron Rathcavan John O'Neill, 3rd Viscount O'Neill Martin O'Neill, Baron O'Neill of Clackmannan (1979–2005) Robert Torrens O'Neill Daniel O'Leary William Hagarty O'Leary Bryan O'Loghlen Colman O'Loghlen Myles O'Reilly William O'Reilly William O'Shea Patrick O'Shaughnessy Richard O'Shaughnessy Eugene O'Sullivan Timothy O'Sullivan William Henry O'Sullivan OA Gordon Oakes (1964–1997) Mark Oaten (1997–2010) OD William Odell OG George Ogle OL William Oldfield (1942–1955) Laurence Oliphant (1865–1869) Charles Silver Oliver Bill Olner (1992–2010) Sarah Olney (2016–2017) ON Richard Onslow, 1st Baron Onslow (1679–1715) Chi Onwurah (2010–present) OP Lembit Öpik (1997–2010) Sally Oppenheim-Barnes, Baroness Oppenheim-Barnes (1970–1987) OR Diana Organ (1997–2005) Sir Charles Ormsby, 1st Baronet David Ormsby-Gore, 5th Baron Harlech (1950–1961) William Ormsby-Gore William Ormsby-Gore, 4th Baron Harlech (1910–1938) William Ormsby-Gore, 2nd Baron Harlech (1841–1852), (1858–1876) OS George Osborne (2001–present) Sandra Osborne (1997–present) OT Sir Richard Ottaway (1983–1987), (1992–2015) Sir Arthur Otway OW Albert Owen (2001–present) David Owen (1966–1992) Idris Owen (1970–1974)
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