A •
Aidan O'Brien (born 1969), Irish racehorse trainer •
Aiden O'Brien, Irish football player •
Alan O'Brien, Irish association football player •
Alex O'Brien (born 1970), American tennis player •
Ambrose O'Brien (1885–1968), Canadian founder of the National Hockey Association •
Andy O'Brien (disambiguation), various •
Anne O'Brien (disambiguation), various •
Arthur O'Brien (1878–1951), New Zealand rugby union fullback •
Austin O'Brien (born 1981), American actor and photographer
B •
Barry O'Brien (born 1957), American TV screenwriter and producer •
Billy O'Brien (baseball) (1860–1911), American baseball player •
Billy O'Brien (footballer), Welsh association football player •
Brendan O'Brien (disambiguation), various •
Brenna O'Brien (born 1991), Canadian actress and voice actor •
Brock O'Brien (born 1988), Australian rules footballer with Fremantle •
Buck O'Brien (1882–1959), pitcher with the Boston Red Sox and the Chicago White Sox •
Burton O'Brien (born 1981), Scottish football player
C •
Casey O'Brien (b. 2001), American ice hockey player •
Cathy O'Brien (athlete) (b. 1967), American long-distance runner •
Cathy O'Brien (conspiracy theorist) (b. 1957), American purported child-abuse victim •
Cecily O'Bryen (1899–1984), British diving champion •
Charles O'Brien (disambiguation), various •
Christian O'Brien (1914–2001), British geologist, author & historian •
Ciaran O'Brien (born 1987), American soccer coach and player •
Cinders O'Brien, John F., or Darby O'Brien (1867–1892), American baseball pitcher •
Clinton O'Brien (born 1974), Australian rugby league footballer •
Conal O'Brien (born 1956), American television director •
Conan O'Brien (born 1963), US comedian and talk show host •
Connor O'Brien (disambiguation) or •
Conor O'Brien (disambiguation), various people •
Cubby O'Brien (born 1946), American drummer and original Mouseketeer
D •
Daniel O'Brien (disambiguation), various •
Danielle O'Brien (born 1990), Australian ice dancer •
Danny O'Brien (disambiguation), various •
Dara Ó Briain, Irish comedian and presenter •
Darcy O'Brien (1939–1998), American true crime author •
Daryl O'Brien (b. 1941), Australian rules footballer •
Dave O'Brien (actor) (1912–1969), American film actor •
Dave O'Brien (sportscaster), American sportscaster •
David O'Brien (disambiguation), various •
Doug Brien (born 1970), American football placekicker •
Don Brien (born 1959), Canadian sprint canoer •
Declan O'Brien (1965–2022), American film and TV writer and producer •
Declan O'Brien (footballer) (born 1979), with Drogheda United •
Dennis O'Brien (disambiguation), various •
Derek O'Brien (disambiguation), various •
Dermod O'Brien (1865–1906), Irish painter •
Donald O'Brien (disambiguation), various •
Doug O'Brien (born 1984), Canadian ice hockey defenceman •
Dylan O'Brien (b. 1991), American actor
E •
Ed O'Brien (b. 1968), English musician •
Edmond O'Brien (1915–1985), American actor •
Edna O'Brien (1930–2024), Irish novelist •
Edward O'Brien (disambiguation), various •
Edwin Frederick O'Brien (born 1939), American Catholic prelate •
Eileen O'Brien (disambiguation), various •
Elaine O'Brien (1955–2014), American politician •
Erin O'Brien (writer), American writer •
Erin Joanne O'Brien (1934–2021), American actress •
Eugene O'Brien (disambiguation), various
F •
Fergal O'Brien (born 1872), Irish professional snooker player •
Fergal O'Brien (trainer) (born 1972), Irish National Hunt trainer •
Fergus O'Brien (1930–2016), Irish politician •
Fitz James O'Brien (1826–1862), American SF and fantasy writer •
Flann O'Brien (Brian O'Nolan, 1911–1966), Irish novelist and satirist
G •
Gareth O'Brien (born 1991), English rugby league footballer •
Geraldine O'Brien (1922–2014), Irish botanical illustrator •
George O'Brien (disambiguation), various •
Ger O'Brien (born Gerard O'Brien, 1984), Irish footballer •
Gerard O'Brien (disambiguation), various •
Geoffrey O'Brien (born 1948), American poet, editor, and film critic •
Glenn O'Brien (1947–2017), American writer, "The Style Guy" •
Gray O'Brien (born Gerard O'Brien, 1968), Scottish actor •
Gavin O'Brien (born 1993), Irish hurler
H • Harry O'Brien, later
Héritier Lumumba (born 1986), Australian rules footballer •
Harry J. O'Brien "Shorty" (1884–1955), American football, basketball, baseball coach •
Helen O'Brien (1925–2005), British nightclub owner and spy •
Henry O'Brien (disambiguation), various •
Hod O'Brien (1936–2016), American jazz pianist •
Hugh O'Brien (1827–1895), mayor of Boston
I •
Iain O'Brien (born 1976), New Zealand cricketer •
Ian O'Brien (born 1947), Australian breaststroke swimmer •
Ignatius O'Brien, 1st Baron Shandon (1857–1930), Lord Chancellor of Ireland, 1913–1918
J •
Jack O'Brien (disambiguation), various •
Jake O'Brien (ice hockey) (born 2007), Canadian ice hockey player •
Jake O'Brien (fighter) (born 1984), American MMA fighter •
Jake O'Brien (footballer) (born 2001), Irish footballer •
James O'Brien (disambiguation), various •
Jamie O'Brien (disambiguation), various •
Jeremiah O'Brien (1744–1818), US Navy officer of the American Revolutionary War •
Jesse O'Brien (disambiguation), various •
Jim O'Brien (disambiguation), various •
Joan O'Brien (1936–2025), American actress and singer •
Joanne O'Brien, portrait and documentary photographer •
Joe O'Brien (disambiguation), various •
Joey O'Brien (born 1986), Irish football player •
John O'Brien (disambiguation), various •
Joseph O'Brien (disambiguation), various
K •
Kate O'Brien (disambiguation) •
Katharine O'Brien, American film director •
Katharine O'Brien (disambiguation), other people of that name •
Katherine O'Brien (born 1963), Canadian pediatric infectious disease physician •
Kathleen O'Brien (1914–1991), Australian illustrator and fashion artist •
Katie O'Brien, British tennis player •
Keith O'Brien (1938–2018), Scottish Roman Catholic prelate •
Ken O'Brien (born 1960), American football quarterback •
Kerry O'Brien (disambiguation), various •
Kevin O'Brien (disambiguation), various •
Kieran O'Brien (born 1973), English actor •
Kim O'Brien, American film and television actress •
Kirsten O'Brien (born 1972), British TV presenter •
Kitt O'Brien (born 1990), American football player •
Kitty Wilmer O'Brien (1910–1982), Irish landscape painter
L •
Larry O'Brien (1917–1990), American politician •
Larry O'Brien (Canadian politician) (born 1949), businessman, mayor of Ottawa •
Laurence O'Brien (1792–1870), Irish merchant and politician in Newfoundland •
Lawrence O'Brien (disambiguation), various :*
Lawrence D. O'Brien (1951–2004), Canadian politician representing Labrador •
Leighton O'Brien (born 1976), American soccer player with the Seattle Sounders •
Lévis Brien (born 1955), Quebec politician •
Leo O'Brien (disambiguation), various •
Leonora O'Brien, Irish pharmacist and entrepreneur •
Leslie O'Brien (1908–1995), Governor of the Bank of England •
Leslie O'Brien (cricketer) (1905–1967), played for New South Wales •
Liam O'Brien (disambiguation), various •
Lucy O'Brien (born 1961), writer on women in music •
Lucy O'Brien (philosopher) (born 1964), at University College, London •
Lucy O'Brien (doctor) (1923–2006), Irish missionary in Africa •
Luke O'Brien (born 1988), English footballer with Bradford City
M •
Margaret O'Brien (born 1937), American actress •
Margaret O'Brien (politician) (born 1973), Michigan Republican •
Maria O'Brien (actress) (1950–2026), American actress and acting coach •
Mariah O'Brien (born 1971), American actress and interior designer •
Mark O'Brien (disambiguation), various •
Mary Eileen O'Brien, American academic administrator •
Matthew O'Brien (mathematician) (1814–1855), Irish mathematician •
Maureen O'Brien (born 1943), English actress in the Doctor Who series •
Michael O'Brien (disambiguation), various •
Michele O'Brien (born 1980), soccer coach and player for Chicago Red Eleven •
Mick O'Brien (disambiguation), various •
Mike O'Brien (hurler) (born 2011) with Glenroe and Limerick •
Miles O'Brien (disambiguation), various •
Mollie O'Brien (born 1952), a folk singer from West Virginia
N •
Niall O'Brien (disambiguation), various •
Natasha O'Brien, an Irish woman attacked by an active-duty Irish soldier •
Nick O'Brien (born 1993), Australian rules footballer for Essendon
O •
Olivia O'Brien (born 1999), American singer and songwriter
P •
Paddy O'Brien (disambiguation), various •
Parry O'Brien (1932–2007), American shot put champion •
Patricia Salas O'Brien (born 1958), Peruvian sociologist and Minister of Education •
Patrick O'Brien (disambiguation), for people with the forename Patrick or Pat •
Pat O'Brien (disambiguation), various •
Paul O'Brien (disambiguation), various •
Peter O'Brien (disambiguation), various •
Phil O'Brien (disambiguation), various
R •
Raymond O'Brien (born 1944), American Roman Catholic priest •
Raymond Moulton O'Brien (1905–1977), British-born American businessman •
Richard O'Brien (disambiguation), various •
Riley O'Brien (born 1995), American baseball pitcher •
Robert O'Brien (disambiguation), various •
Ron O'Brien (disambiguation), various •
Roy O'Brien (born 1974), Irish football player
S •
Saylor O'Brien (born 2003), American para-alpine skier •
Scott O'Brien (born 1957), American football player, coach and scout •
Sean O'Brien (disambiguation) •
Sean Patrick O'Brien (1988–2023), American professional wrestling referee •
Shane O'Brien (disambiguation), various •
Shannon O'Brien (disambiguation), various •
Sicele O'Brien (1887–1931), Irish woman aviation pioneer •
Simon O'Brien (disambiguation), various •
Soledad O'Brien (born 1966), American woman television journalist •
Stephen O'Brien (born 1957), UK conservative politician for Eddisbury •
Stuart O'Brien (1906–2004), American film editor •
Stuart O'Brien (stage) (1833–1883), Australian actor
T •
Terence O'Brien (disambiguation), various •
Thomas O'Brien (disambiguation), various •
Tim O'Brien (disambiguation), various •
Timothy O'Brien (theatre designer) (1929–2022), British theatre designer •
Timothy O'Brien (endocrinologist), Irish professor •
Timothy L. O'Brien (born 1961), American journalist •
Tina O'Brien (born 1983), English actress •
Tom O'Brien (actor) (b. 1965), American film actor •
Tom O'Brien (American football) (b. 1948), coach at North Carolina State University •
Tom O'Brien (outfielder) (1873–1901), baseball outfielder •
Tom O'Brien (second baseman) (1860–1921), 19th-century baseball player •
Tom O'Brien (trade unionist) (1900–1970), British trade unionist and Member of Parliament •
Tommy O'Brien (baseball) (1918–1978), baseball outfielder
U •
Una O'Brien, British civil servant
V •
Vincent O'Brien (disambiguation), various •
Virginia O'Brien (1919–2001), American actress and comic, "Frozen Face" singer
W •
Walter O'Brien (born 1975), Irish businessman and computer specialist •
Walter A. O'Brien (1914–1998), American Progressive Party politician •
William O'Brien (disambiguation), various •
Willis H. O'Brien (1886–1962), American motion picture special effects pioneer
Z •
Zach O'Brien (born 1992), professional ice hockey player ==As first or middle names==