A •
Alan O'Neill (footballer, born 1957), Irish football player •
Alan O'Neill (footballer, born 1973), Irish football player •
Alexander O'Neal (born 1953), American musician •
Alexandre O'Neill (1924–1986), Portuguese writer • Alexander O'Neill aka
Alexx O'Nell (born 1980), American musician and actor •
Amber O'Neal (born 1974), American professional wrestler •
Amos O'Neal, American politician •
Amy O'Neill (born 1971), an actress/performer •
Ana María O'Neill, an educator, author and advocate of women's rights •
Andrew O'Neill (born 1979), English vegan, anarchist, transvestite, stand-up comedian, musician and writer •
Anthony O'Neill (born 1964), Australian fiction writer •
Aisling O'Neill, Irish actress •
April O'Neil, a fictional character in the
Teenage Mutant Ninja Turtles franchise •
Arthur Joseph O'Neill (1917–2013), an American bishop of the Roman Catholic Church •
Arthur O'Neill (1876–1914), was an Irish Ulster Unionist Party politician •
Arturo O'Neill (1736–1814), an Irish-born colonel who served the Spanish crown as governor of several places in New Spain (1781–1794)
B •
Barbara O'Neil, American film and stage actress •
Bernie O'Neill (politician), member of the Pennsylvania House of Representatives •
Bernie O'Neill (bowls), Northern Irish lawn bowler •
Bernie O'Neill (Gaelic footballer) (born 1945), Irish Gaelic footballer •
Bill O'Neill (1880–1920), Canadian-born Major League Baseball player •
Bill O'Neill (born 1981), American professional bowler •
Billy O'Neill (rugby) (1878–1955), Welsh international rugby union player •
Billy O'Neill (footballer), Irish professional footballer •
Birch O'Neal (c. 1913–1995), FBI/CIA agent •
Brendan O'Neill (businessman) (born 1948), British business executive •
Brendan O'Neill (journalist), English journalist •
Brian O'Neill (ice hockey, born 1929), Canadian executive within the National Hockey League •
Brian O'Neill (ice hockey, born 1988), American ice hockey player •
Brian O'Neill (1574), chief of the O'Neills of Clanaboy, surrendering his title to Sir Philip Sidney for a knighthood in 1567 •
Brian O'Neill (superintendent) (1941–2009), American superintendent of the Golden Gate National Recreation Area •
Brian O'Neill (American football) (born 1995), American football player •
Bryan O'Neil (1905–1954), British archaeologist and historian •
Buckey O'Neill (1860–1898), American soldier, sheriff, newspaper editor, miner, politician, gambler and lawyer •
Byron O'Neill (born 1970), American artist
C •
Calvin O'Neal, American football linebacker •
Carol O'Neal (born 1948), American model and Playboy magazine's Playmate of the Month in July 1972 •
Catherine O'Neill (cricketer), New Zealand-born Irish cricketer •
Cathy O'Neil, American mathematician •
Charles Duncan O'Neal (1879–1936), Barbados politician and physician •
Charles O'Neal (1904–1996), American film and television screenwriter •
Christopher John O'Neill, Broadway actor •
Chris O'Neill, Irish animator and YouTuber •
Connor O'Neill, fictional Northern Irish character in the Australian soap opera
Neighbours •
C. William O'Neill (1916–1978), American politician •
Carlos O'Neill (1760–1835), titular head of the Clanaboy O'Neill dynasty •
Cecily O'Neill, authority on Process drama and the arts in education •
Charles O'Neill (musician), Canadian bandmaster and composer •
Charles O'Neill (engineer) (1828–1900), Australasian engineer, inventor, parliamentarian and philanthropist •
Charles H. O'Neill (c. 1800–1897), Irish-born American politician and mayor •
Charles O'Neill (Pennsylvania politician) (1821–1893), American politician •
Charles O'Neill, 1st Earl O'Neill (1779–1841), British politician, peer and landowner •
Chloe Ann O'Neil (1943–2018), New York politician •
Christopher O'Neill (born 1974), British-American businessman and the husband of Princess Madeleine of Sweden •
Cian O'Neill, Irish Gaelic footballer, coach and manager •
Colm O'Neill (Ballyclough Gaelic footballer) (born 1988), Irish sportsman •
Colm O'Neill (Midleton Gaelic footballer) (born 1964), Irish sportsman •
Con O'Neill (actor) (born 1966), British actor •
Con O'Neill (diplomat) (1912–1988), British civil servant and diplomat •
Conn (Constantine) O'Neill, titular head of the Clanaboy O'Neill dynasty
D •
Dave O'Neal (1937–2021), American politician, Lieutenant Governor of Illinois •
Deltha O'Neal (born 1977), American football player •
Damian O'Neill (born 1961), lead guitarist in the pop-punk band, The Undertones •
Dan O'Neill (born 1942), American underground cartoonist •
Dan O'Neill (writer), American journalist and writer •
Daniel O'Neill (painter) (1920–1974), Irish Romantic painter •
Daniel O'Neill (editor), Irish-born American newspaper editor and owner •
Daria O'Neill (born 1971), American radio and television personality •
Darren O'Neill, an Irish boxer •
Dennis O'Neill (disambiguation), several people •
Dermot O'Neill (disambiguation), several people •
Diarmuid O'Neill (1969–1996), English-born volunteer in the Provisional Irish Republican Army •
Dick O'Neill (1928–1998), American stage, film and television actor •
Don O'Neill (artist), American watercolorist and architect •
Dónal O'Neill (1967–2023), Irish Gaelic footballer •
Donal O'Neill (Gaelic footballer) (born 1988), Irish Gaelic footballer for Galway •
Donal O'Neill (swimmer) (born 1980), Irish swimmer •
Douglas F. O'Neill (born 1968), American Thoroughbred horse trainer
E •
Eamon O'Neill (born 1944), Northern Irish nationalist politician in Northern Ireland •
Eamonn O'Neill (died 3 November 1954), Irish Cumann na nGaedhael and later Fine Gael party politician •
Edward O'Neill (disambiguation), several people •
Ed O'Neill (born 1946), American actor • Ed O'Neal (1936–2022), American musician, of the
Dixie Melody Boys •
Edward J. O'Neill (general) (1902–1979), American US Army officer •
Edward L. O'Neill (1903–1948), American politician •
Edward O'Neill, 2nd Baron O'Neill (1839–1928), Irish peer and politician •
Eliza O'Neill (1791 – 29 October 1872), Irish actress, later baronetess •
Elizabeth O'Neill Verner (1883–1979), artist, author and lecturer •
Ella O'Neill, mother of playwright Eugene O'Neill and wife of actor James O'Neill •
Emmett O'Neill (1918–1993), American Major League Baseball pitcher •
Eric O'Neill (born 1973), American former FBI operative •
Eugene M. O'Neill (1850–1926), Irish-born American lawyer and newspaper owner •
Eugene O'Neill (hurler) (born 1978), Irish sportsperson •
Eugene O'Neill (1888–1953), American playwright, and Nobel laureate in Literature •
Eunan O'Neill (born 1982), Northern Irish television presenter •
Evan O'Neill Kane (1861–1932), surgeon working in Pennsylvania, US •
Edward Asbury O'Neal (1818–1890), American Confederate general during the American Civil War •
Emmet O'Neal (1853–1922), American Democratic politician who was Governor of Alabama
F •
Frank O'Neal, American cartoonist •
Frederick O'Neal (1905–1992), American actor and television director •
Fabián O'Neill (born 1973), Uruguayan former football midfielder •
Felim O'Neill of Kinard, Irish nobleman who led the Irish Rebellion of 1641 in Ulster •
Francis O'Neill (1848–1936), Irish-born American police chief and author of several Irish music collections •
Frank "Buck" O'Neill (1875–1958), American head football coach •
Frank O'Neill (footballer, born 1940) (born 1940), Irish footballer
G •
Gail O'Neill, American model and television journalist •
Gary O'Neill, various people •
Gene O'Neill, American novelist •
George Bernard O'Neill (1828–1917), Irish genre painter •
George O'Neill (footballer, born 1942) (born 1942), Scottish footballer who played and managed in the US in his later career •
George O'Neill (footballer, born 1923) (1923–2003), English footballer •
Gerard K. O'Neill (1927–1992), American scientist •
Gerard M. O'Neill (1942–2019), American journalist and writer •
Griffin O'Neal (born 1964), American actor •
Gwendolyn O’Neal (born 1946), American academic administrator and home economist
H •
Harriet O'Neill, American judge •
Harry O'Neill (disambiguation), several people •
Heather O'Neill (born 1973), Canadian novelist, poet, short story writer, screenwriter and journalist •
Henrique O'Neill, 1st Viscount of Santa Mónica, Portuguese noble and politician •
Henry O'Neill (disambiguation), several people •
Holly O'Neill (born 1998), Canadian soccer player •
Howard S. O'Neill (1883–1966), American politician and lawyer •
Hugh McShane O'Neill, Irish nobleman and rebel in the 16th and 17th centuries •
Hugh O'Neill (disambiguation), several people •
Hugo José Jorge O'Neill (1874–1940), Portuguese nobleman
I •
Isabelle Ahearn O'Neill (1880–1975), stage and screen actor and Rhode Island legislator •
Israel C. O'Neal (1818–1899), American politician from Virginia •
Ivan O'Neal, Vincentian political leader
J •
Jack O'Neill, a fictional character in the Canadian-American SyFy television series
Stargate SG-1 •
Jamie O'Neal (born Jamie Murphy, 1968), Australian country singer and songwriter •
Jermaine O'Neal (born 1978), American NBA basketball player •
Jim O'Neal (born 1948), American blues expert, writer, record producer and record company executive •
Joseph T. O'Neal, American politician •
Johnny O'Neal, American jazz pianist •
Jack O'Neill (baseball) (1873–1935), Irish-American baseball catcher •
Jack O'Neill (businessman) (1923–2017), American businessman •
Jack O'Neill (disambiguation) •
Jacquie O'Neill (born 1969), English illustrator •
James O'Neill (disambiguation), several people •
Jamie O'Neill (born 1962), Irish authoer •
Jamie O'Neill (snooker player), English snooker player •
Jan Lehane (born 1941), married name O'Neill, Australian tennis player •
Jeff O'Neill (born 1976), Canadian broadcaster and former ice hockey player •
Jeffrey O'Neill (disambiguation), several people •
Jennifer O'Neill, American actress and model •
Jevon O'Neill, British film director and producer •
Jim O'Neill (disambiguation), several people •
Jimmy O'Neill (footballer, born 1931) (1930–2007), Irish football goalkeeper •
Jimmy O'Neill (footballer, born 1941), Northern Irish footballer •
João O'Neill •
João Pedro Torlades O'Neill •
Joaquim Torlades O'Neill •
Joe O'Neill, English footballer •
John Johnston O'Neill (1886–1966), Canadian geologist and academic •
John Joseph O'Neill (journalist) (1889–1953), American journalist •
John Joseph O'Neill (British politician) (1888–1953), English Liberal MP •
John Joseph O'Neill (American politician) (1846–1898), U.S. Representative from Missouri •
John O'Neill (disambiguation), several people •
John Raymond O'Neill, Canadian politician •
Jonjo O'Neill (jockey) (born 1952), Irish National Hunt racehorse trainer and jockey •
Jorge Maria O'Neill •
Jorge Torlades O'Neill I •
Jorge Torlades O'Neill II •
José Carlos O'Neill •
José Maria O'Neill •
Josh O'Neill (born 1988), American wheelchair rugby player •
Joseph O'Neill (disambiguation), several people •
Julian O'Neill (New Zealand rugby league), New Zealand rugby league footballer who played in England •
Julian O'Neill, Australia rugby league footballer •
Juliet O'Neill, Canadian journalist
K •
Kathleen O'Neal Gear (born 1954), American writer •
Kate Tenforde (née O'Neill; born 1980), American long-distance runner •
Katie O'Neill, illustrator and writer from New Zealand •
Keith O'Neill (disambiguation), several people •
Ken O'Neal (born 1962), American football player •
Kevin O'Neill (disambiguation), several people •
Kim L. O'Neill, Irish biologist in the United States •
Kitty O'Neil (1946–2018), American stuntwoman and racer
L •
Leon O'Neal Jr. (born 1998), American football player •
Leslie O'Neal (born 1964), American football player •
Laurence O'Neill, Irish politician •
Lawrence Joseph O'Neill, American judge •
Lawrence O'Neill (disambiguation), several people •
Linda O'Neill, Australian soccer player •
Louis O'Neill (diplomat), American diplomat and attorney •
Luke O'Neill (disambiguation), several people
M •
Madeline O'Neill (born 1867/68), British tennis player •
Maggie O'Neill, British actress •
Máire O'Neill (born 1978), Irish data encryption academic •
Maire O'Neill (1886– 1952), Irish actress •
Margaret O'Neill Eaton (1799–1879), wife of John Eaton, involved in the Petticoat Affair •
María de Mater O'Neill (born 1960), Puerto Rican artist, designer and educator •
Maria O'Neill, Portuguese member of the Clanaboy O'Neill dynasty •
Mark O'Neill (disambiguation), several people •
Martha Mary O'Neill, aka 'Mother Patricia', Irish-Australian Sister of Charity •
Martin O'Neill, Baron O'Neill of Clackmannan •
Martin O'Neill, Northern Irish footballer and manager •
Marty O'Neill (born 1965), Canadian lacrosse player and manager •
Mary Auguste O'Neill •
Mary Devenport O'Neill, Irish poet •
Mary O'Neill (Canadian politician), Canadian politician •
Mary-Anne O'Neill, Australian politician •
Mary Lovelace O'Neal, American artist •
Mary Thomas O'Neal (1887 – after 1974), Welsh-born American labor activist •
Maston E. O'Neal Jr. (1907–1990), American politician •
Matthew O'Neill (disambiguation), several people •
Maurice O'Neill (Irish republican), (d.1942), Executed Irish Republican •
Melinda O'Neal, American conductor of choral music •
Merlin O'Neill (1898–1981), Commandant of the United States Coast Guard 1950 to 1954 •
Michael O'Neill (disambiguation), several people •
Michelle O'Neill, Irish politician, deputy First Minister of Northern Ireland since 2020, Vice President of Sinn Féin since 2018 •
Mike O'Neal (born 1951), Kansas Republican politician •
Mildred O'Neill (1914? – 2003), wife of Speaker of the United States House of Representatives Tip O'Neill •
Moira O'Neill, pseudonym of Agnes Shakespeare Higginson (1864–1955), Irish-Canadian poet •
Morgan O'Neill, Australian writer, director, actor and producer
N •
Nathan O'Neill, Australian cyclist •
Nicholas O'Neill (disambiguation), several people •
Norm O'Neill, Australian cricketer •
Norman O'Neill (1875–1934), English composer and conductor
O •
Onora O'Neill, Baroness O'Neill of Bengarve •
Oona O'Neill, American actress •
Owen Roe O'Neill (c.1585 – 1649), Gaelic Irish soldier •
O'Neal Compton (1951–2019), American film and television actor •
O'Neill Donaldson (born 1969), English footballer •
O'Neill Spencer (1909–1944), American jazz drummer and singer •
Sir Neil O'Neill, Irish chieftain
P •
Patrice O'Neal (1969–2011), American comedian •
Patrick O'Neal (disambiguation), several people •
Peggy O'Neal (disambiguation), several people •
Pete O'Neal (born 1940), American Black Panther Party member •
Pat O'Neill (disambiguation), several people •
Patrick O'Neill (disambiguation), several people •
Paul O'Neill (disambiguation), several people •
Pauline O'Neill (disambiguation), several people •
Pearse O'Neill, Irish Gaelic footballer •
Peggy O'Neil (1898–1960), Irish-American actress •
Peter O'Neal, American politician •
Peter O'Neill, former prime minister of Papua New Guinea •
Phelim (Felix) O'Neill •
Phelim Caoch O'Neill (1517–1542), prince of the Cenél nEógain •
Phelim O'Neill, 2nd Baron Rathcavan R •
Raiqwon O'Neal (born 2000), American football player •
Ralph Ambrose O'Neill (1896–1980), American flying ace from World War I •
Rebecca O'Neill (born 1981), New Zealand football player •
Richard O'Neill (disambiguation), several people •
Riley O'Neill (born 1985), Canadian soccer player •
Robert O'Neal (American football) (born 1971), former American football cornerback •
Robert O'Neal (murderer) (1961–1995), American white supremacist and convicted murderer executed in Missouri •
Robert O'Neill (disambiguation), several people •
Robin O'Neil, British historian •
Rose O'Neill (1874–1944), American illustrator •
Ryan O'Neill (disambiguation), several people •
Ralph T. O'Neal (1933–2019), British Virgin Islands politician •
Reagan O'Neal, one of several pseudonyms of James Oliver Rigney Jr (1948–2007), American writer •
Ronan O'Neill, Irish Gaelic footballer •
Ron O'Neal (1937–2004), American actor, director and screenwriter •
Rose O'Neal Greenhow (1817–1864), Confederate spy •
Ryan O'Neal (born 1941), American actor
S •
Séamus Ó Néill (1910–1986), Irish writer •
Shareef O'Neal (born 2000), American basketball player and son of Shaquille •
Shaquille O'Neal (born 1972), American basketball player •
Stanley O'Neal (born 1951), American business executive •
Steve O'Neal (born 1946), American football punter •
Seán O'Neill (born 1938), Northern Irish Gaelic footballer •
Sean O'Neill (table tennis) (born 1967), American table tennis player and coach •
Shane O'Neill (Irish chieftain) (c. 1530–1567), Irish chief of the O'Neill clan of Ulster •
Shane O'Neill (Irish exile) (c. 1599 – 29 January 1641), youngest son of Hugh O'Neill, Earl of Tyrone •
Shane O'Neill (Cork hurler) (born 1986), Irish sportsperson •
Shannon O'Neill (comedian), American comedian •
Shannon O'Neill (politician) (born 1937), Canadian politician •
Sharon O'Neill (born 1952), New Zealand singer-songwriter and pianist •
Sid O'Neill (1888—1915), Australian rules footballer •
Simon O'Neill (born 1971), New Zealand-born operatic tenor •
Stephen O'Neill (born 1980), Irish Gaelic footballer •
Steve O'Neill (1891–1962), American catcher, manager, coach and scout in Major League Baseball •
Steve O'Neill (owner) (1899–1983), American owner of a professional baseball team •
Steve O'Neill (rugby league) (born 1958), English rugby league footballer •
Susie O'Neill (born 1973), Australian swimmer
T •
Tara Lynne O'Neill, Northern Irish actress •
Ted O'Neill, Dean of Admissions at the University of Chicago •
Terence O'Neill, Baron O'Neill of the Maine (1914–1990), the fourth Prime Minister of Northern Ireland •
Terry O'Neill (feminist) (born c. 1953), American attorney, professor and activist for social justice •
Terry O'Neill (martial artist) (born 1948), English actor and martial artist •
Terry O'Neill (photographer) (1938–2019), English photographer •
Thomas Newman O'Neill Jr. (1928–2018), American federal judge •
Thomas O'Neill (journalist) (1904–1971), American journalist •
Thomas O'Neill (Canadian politician) (1882–1965), Canadian politician •
Thomas P. O'Neill III (born 1945), American politician •
Tim O'Neill (Canadian football) (born 1979), Canadian football player •
Timothy O'Neill (soccer) (born 1982), American soccer player •
Tip O'Neill (1912–1994), American politician •
Tip O'Neill (baseball) (1858–1915), Canadian left fielder in Major League Baseball •
Titus O'Neil (born 1977; real name Thaddeus Bullard), American professional wrestler •
Todd O'Neill (born 1982), American singer •
Tom O'Neill (ice hockey) (1923–1973), Canadian ice hockey player •
Tommy O'Neill (born 1955), Scottish football midfielder •
Tony O'Neill, New York-based musician and author •
Tatum O'Neal (born 1963), American actress •
Tirlough Brassileagh Ó Neill, son of Phelim Caoch O'Neill, Prince of the Cenél nEógain •
Turlough Luineach Ó Neill (1532–1595), Irish earl of the Clan-Connell, inaugurated as the King of Tyrone •
Ty O'Neal (born 1978), American actor
W •
Ward O'Neill (born 1951), Australian illustrator, caricaturist and cartoonist •
Wes O'Neill (born 1986), Canadian ice hockey player •
Willa O'Neill, New Zealand actress •
William O'Neill (Connecticut politician) (1930–2007), American Governor of Connecticut •
William O'Neill (Ohio jurist) (born 1947), American lawyer, jurist and appellate judge •
William O'Neill, 1st Baron O'Neill (1813–1883), Anglo-Irish hereditary peer, clergyman and musical composer •
William T. O'Neil (1850–1909), New York politician •
William J. O'Neil, American entrepreneur, stockbroker and writer •
William O' Neil (1848–?), member of the Wisconsin Legislature
Y •
Yvonne O'Neill (1936–2010), Canadian politician