O'Sullivan is an Irish surname, associated with the southwestern part of Ireland, originally found in County Tipperary before the Anglo-Norman invasion then in the counties of Cork and Kerry, which due to emigration is also common in Australia, North America and The UK. Emigrants often suppressed the "O" to make the name Sullivan; the two names are both anglicised versions of the Irish name Ó Súilleabháin.
In the Irish language the word Ó means 'grandson' and can be found in many Irish surnames. It has been anglicised as O'. When placed before the genitive form of Súilleabhán, which is Súilleabháin, it can be translated as grandson of. While the use of an apostrophe is a common convention in English, the apostrophe is never used in the original Irish language version of the name.
Ó Súilleabháin (the genitive form of súilleabhán being súilleabháin) probably derives from the Irish Ó which comes from Ua meaning grandson and súildhubhán meaning little dark-eyed one, from the Irish súil meaning eye followed by dubh meaning black and the diminutive suffix -án.
The motto for the O'Sullivans is "An Lámh Fhoisteanach Abú" which translates as "The Steady Hand to Victory"
Notable people named O'Sullivan include:
- Aine O'Sullivan Actress/Artist. Born Cork. Co-Founder of The Green Heart Company, An Irish Artists Collective. Est 2007.
- Dan O'Sullivan (born 1968), professional NBA player
- David O'Sullivan (born 1944), New Zealand cricket player
- Denis O'Sullivan (born 1948), Irish golfer
- Denis J. O'Sullivan (1918–1987), Irish Fine Gael TD from Cork
- Donal O'Sullivan (1561-1613), Irish chieftan
- Diarmuid O'Sullivan (born 1978), Irish sportsman
- Eddie O'Sullivan (born 1958), head coach of the Ireland rugby union team
- Edward William O'Sullivan (1846–1910), Australian journalist and politician
- Eugene D. O'Sullivan (1883–1968), American Democratic Party politician from Nebraska
- Fionn O'Sullivan (1805-1901), Helped devolop Dog therioum
- Gearóid O'Sullivan (1891–1994), Irish teacher, Irish Republican Army officer, barrister and Sinn Féin and Fine Gael politician
- Gerald Robert O'Sullivan VC (1888–1915), Irish soldier in the British Army,recipient of the Victoria Cross
- Gerry O'Sullivan (1936–1994), Irish Labour Party TD
- Gilbert O'Sullivan (born 1946), Irish-born, UK-based singer-songwriter, who had several hits in the 1970s
- Jacquie O'Sullivan (born 1960), British singer and songwriter.
- Jan O'Sullivan (born 1950), Irish Labour Party politician, currently a Teachta Dála (TD) for Limerick East
- Jeremiah O'Sullivan (born 1842 in Ireland), American Roman Catholic bishop
- Jerry O'Sullivan, contemporary Irish-American musician, plays bagpipes and uilleann pipes
- John O'Sullivan, a name shared by a number of notable men
- J.T. O'Sullivan (born 1979), American football quarterback for the San Francisco 49ers
- Maggie O'Sullivan (born 1951), British poet, performer and visual artist
- Lance O'Sullivan (born 1963), retired New Zealand jockey
- Marcus O'Sullivan (born 1961), Irish coach and former middle distance runner based in the United States
- Maureen O'Sullivan (1911–1998), Irish cinema actor
- Mícheál Ó Súilleabháin, Irish composer and musician.
- Muiris Ó Súilleabháin, author of autobiography Fiche Blian ag Fás (Twenty Years A-Growing)
- Owen Roe O'Sullivan (1748-1782), Irish Gaelic poet
- Pat O'Sullivan, American golfer who won the 1951 Titleholders Championship
- Patrick O'Sullivan (born 1985), Los Angeles Kings Left Wing Canadian hockey player in the United States
- Peter O'Sullivan (born 1943) in Cashel, County Tipperary) is a former Irish sportsperson.
- Richard O'Sullivan (born 1944), English actor, notable for his sitcom roles in the 1970s and 1980s.
- Ronnie O'Sullivan (born 1975), English professional snooker player
- Seamus O'Sullivan (1879–1958), Irish poet and editor of The Dublin Magazine
- Father Sean O'Sullivan (1952–1989), Canadian politician and religious leader
- Shawn O'Sullivan (born 1964), Canadian boxer
- Sonia O'Sullivan (born 1969), Irish Olympic runner
- Terence Patrick O'Sullivan (1913–1970), civil engineer
- Timothy (Ted) O'Sullivan (1899 –1969), Fianna Fáil Party politician
- Timothy H. O'Sullivan (c. 1840–1882), photographer
- Toddy O'Sullivan (born 1934), Irish Labour Party politician
- Wayne O'Sullivan (born 1974), Irish soccer player in Australia