The O'Tooles of Leinster, one of the leading families of that province, are descended from Tuathal Mac Augaire, King of Leinster (died 958), who belonged to the Uí Dúnlainge dynasty. The name is an anglicisation of the Irish Ó Tuathail.
The first to use the surname in true hereditary fashion appears to have the grandson of Tuathal Mac Augaire, Doncaon, slain at Leighlin in 1014.
Their original territory comprised the southern part of the present County Kildare but they were driven from it during the Anglo Norman invasion and settled in the mountains of what is now County Wicklow around Glendalough through the 12th century. The area they controlled was roughly identical to the old diocese of Glendalough, with the centre of their power in the region around the Glen of Imaal.
Despite the proximity of Dublin, the centre of English rule in Ireland, the Ó Tuathail's maintained a fierce independence, and were a source of great fear to the inhabitants of Dublin and the Pale for almost four centuries. With their kinsmen the O'Byrne family, they were noted for their tough resistance to English domination, including exercising great influence over the foundation of the Confederation of Kilkenny in 1642 in what had become Confederate Ireland.
At the start of the 16th century, there were five great houses, all, owing allegiance to "The O'Toole of Powerscourt" as the recognized chief:
- O'Toole of Castleruddery, residing in Glen Imaile.
- O'Toole of O'Toole's Castle, Ballymacledy, (now Upper Talbotstown), Glen Imaile.
- O'Toole of Carnew Castle.
- Art Oge O'Toole of Castle Kevin, Fertie.
- Tirlogh O'Toole of Powerscourt, Feracualan.
- O'Toole of Omey, Iar Connaught, with other minor houses of the family such as OToole of Ballineddan and Brittas, in the Glen Imaile; O'Toole of Toolestown, near Dunlavin; O'Toole of Glengap, or Glen of the Downs (as it is now called); and a few others.
At the start of the 16th century, the leading branches of the clan were to a certain extent independent of each other; they were all bound to protect themselves; but in external matters affecting the whole clan they were bound to obey the head of the sept.
Throughout their history the family were famous as soldiers, from fighting the English in the glens of Wicklow to serving in the armies of other Catholic European countries in the 18th century, such as France and Spain.
The descendants of the sept took the name O'Toole, although the name is now rare without the prefix 'O'. The tradition of surnames in Ireland developed spontaneously, as the population increased and the former practice, first of single names and then of ephemeral patronymics or agnomina of the nickname type proved insufficiently definitive. At first the surname was formed by prefixing 'Mac' to the father's Christian name or 'Ó 'to that of a grandfather or earlier ancestor.
The following is a list of names that are related to O'Tuathail. This is not a complete list; there may be other names.
- Saint Laurence O'Toole was an archbishop of Glendalough and in 1171, while he was Archbishop of Dublin he took up arms against the Anglo Norman invaders.' He was canonized in 1225 by Pope Honorius III.
- Mór Ní Tuathail (c. 1114–1191) was a Queen-consort of Leinster as the first wife of King Diarmait Mac Murchada. Mór was the mother of Aoife of Leinster, the wife of Richard de Clare, Earl of Pembroke, known to history as Strongbow.
- Colonel John O'Toole of the Irish Brigade in France was created a count and is the ancestor of the present Count O'Toole of Limoges.
- Sergeant O'Toole of the 9th Queen's Royal Lancers of the British Army was awarded a Victoria Cross for conspicuous bravery in the Zulu War on 3 July 1879.
- John Lawrence Toole (1830–1906) the comedian, born in London. He went to the City of London School, and in 1853 gave up his desk in a wine merchants to become an actor. He first played at Ipswich and in London at the St. James's Theatre in 1854. In 1874-75 he played in the United States, and in 1890 in Australia. In 1879 he became lessee of the Folly Theatre, which he enlarged, changing the name to 'Toole's Theatre'.
- Peter O'Toole (born 2 August 1932) is a noted Irish stage and screen actor. He has received three Golden Globes, an Emmy Award and eight Oscar nominations. He was awarded an honorary Oscar for his body of work in 2003. He starred in such films as Lawrence of Arabia, The Lion in Winter, and Goodbye, Mr. Chips.
- Gerard Toal (Irish: Gearóid Ó Tuathail) (born 1962) is a Professor of Government and International Affairs in Washington DC
- Fintan O'Toole is an award winning Irish journalist, author and critic, best known for his work with The Irish Times.
- Michelle O'Toole is an award-winning interior-designer. Best known for her work with the Baltimore Ravens, Saint Louis Rams, World Wide Technologies, and Ascension Health. She now owns her own Interior Design Firm, 'O'Toole Design Associates' which specializes in modern commercial interior design; under the slogan, "we make space work."
- Gary O'Toole is a former World champion and represented Ireland twice in the Olympics, 1988 and 1992. Now a leading Orthopaedic Consultant in Ireland.
- Mark O'Toole is the former bassist and a founding member of 1980s pop band, Frankie Goes to Hollywood.
- Daddy O'Toole - concert hall owner in Dublin in the 1900s, and Godfather to the local area, put on performances nightly many of which included Kay O'Toole, the contortionist, and music by Martin O'Toole, father of 13, of whom Imelda O'Toole is the youngest. Imelda's children are heirs to the multi award winning company COOK www.cookfood.net being related via Penfold lines. COOK recently came in the top 50 companies to work for in 2015. Martin O'Toole's brother, Patrick O'Toole was a decorated soldier for the British army in WW2.
- Dean Michael O' Toole - Army veteran that served in the Royal Logistics Corp as a Vehicle Support Specialist (V.S.S). Now a renowned entrepreneur within the UK that supports local businesses and start ups with web design and marketing in Southampton.
- Amy O'Toole- TEDGlobal speaker
- Darrin O'Toole- Comic book writer, American Football Coach at Trinity College Dublin.
- O'Toole, Patrick Laurance (1890). History of the Clan O'Tool and other Leinster Septs. Dublin: M. H. Gill and son; New York, Benziger brothers; [etc., etc.]
This article incorporates text from a publication now in the public domain: "History of the Clan O'Tool and other Leinster Septs" by Patrick Laurance O'Toole