O'Brien Surname Meaning, History & Origin

O’Brien Surname Meaning

The early history of the O’Brien clan is as a Dalcassian tribe in SW Ireland and then with Brian Boru, the legendary king of Ireland who defeated the Norsemen at Clondorf in 1014 but died in the process. The Ui Braians ruled over Munster after Brian Boru’s death and, as O’Briens, emerged as one of the chief dynastic families of Ireland.

Today, due to emigration, there are more O’Briens outside Ireland than within, with the largest number being in America. There are many name variants of O’Brien around the world, including Bryan, McBryan, O’Brian, O’Bryan, Bryant, and Breen.

O’Brien Surname Resources on The Internet

O’Brien Surname Ancestry

  • from Ireland (Munster)
  • to America, Canada and New Zealand

Ireland.  The Rock of Cashel in Tipperary was the traditional seat of the Kingdom of Munster, which the O’Briens would hold until the 12th century.  Two early chronicles of those times were Cogad Gaedhil re Gallaibh, written in 1016, and Caithreim Tordhealbaigh, written in 1276. 

After that time the territory was divided and they ruled over the kingdom of Thurmond in present-day Clare instead.  Their ancestral home was Dromoland castle and the O’Brien rule would last until 1542 when Morrough O’Brien surrendered its sovereignty to the new English kingdom of Ireland under Henry VIII.

O’Brien Branches.  Over the subsequent centuries there were to be many O’Brien branches. The Earls of Thurmond, representing the main descent, did tend to side with the English. Other O’Briens, although they had accepted English titles, often ended up opposing the English cause:

  • Murrough O’Brien, the Earl of Inchiquin, having supported the English in 1641, switched sides and left Ireland for France and French service in 1650, although his grandson was later to return in 1703.
  • while the Viscounts Clare left in 1690 and never returned.  They raised the famous Irish brigade known as Clare’s Dragoons and were fighting for France until the last of them died in 1774.

The O’Briens at Comeragh castle in Waterford were almost wiped out by Cromwell in 1656. After taking the castle, he hanged four of the O’Brien brothers. The fifth, John, managed to escape and from him came the O’Briens of Ballyetragh.

The history of the O’Brien clan, up to the end of the 18th century, was first compiled by John O’Donoghue in the book he published in 1860.  A later account is Iain Gray’s 2008 book O’Brien: The Origins of the O’Brien Family.

Later History.  There were O’Briens supporting the British rule.  Sir Timothy O’Brien, born in Tipperary in 1787, was an MP, mayor of Dublin, and made a baronet.  Subsequent O’Briens of this line were military men in the British army.

However, from an O’Brien gentry line in Clare, came William Smith O’Brien, an Irish nationalist and one of the leaders of the Young Ireland rebellion of 1848.  This led to his arrest, trial, and transportation to Tasmania.

His line nevertheless did continue in Ireland:

  • his daughter Charlotte O’Brien, born in Limerick in 1845, became involved in the campaign to improve the standard of Irish emigrant ships.
  • and his grandson Dermond O’Brien, also born in Limerick, was a leading portrait painter in Dublin for close on forty years.

Other O’Briens of varying backgrounds also became engaged in the cause of Irish nationalism.  William O’Brien from Cork founded the United Irish League in 1898 to press for land reform and home rule.  In 1920 Arthur Griffith said of O’Brien:

“The task of William O’Brien’s generation was well and bravely done.  Had it not been so, the work we are carrying out in this generation would have been impossible.  In that great work none of Parnell’s lieutenants did so much as William O’Brien.”

Today in Ireland, O’Briens are mainly found around Dublin and in the Munster counties of Clare, Limerick, and Cork.

America. A number of O’Briens came to America in the second half of the 18th century, including Morris O’Brien who came to Machias in Maine:

  • his son Captain Jeremiah O’Brien was one of the early American heroes of the Revolutionary War. In 1775 he captured a British armed schooner off Machias in the first naval engagement of the war.
  • while Jeremiah’s son Jeremiah ran a lumber manufacturing and shipping business in Machias and was active in local politics.

Born in Ireland in 1827, Hugh O’Brien moved with his parents to Boston when he was five.  He prospered there as a printer. In 1885, he took the office of mayor of Boston, the first Irish-born and the first Catholic to do so in a city previously run by native-born Protestants.

A much later Boston celebrity is the talk-show host Conan O’Brien who grew up in a middle-class family in Brookline. His forebears had immigrated to Boston from county Kerry at the time of the potato famine.

Canada. The O’Brien name in various forms was evident in Newfoundland by the late 18th century.  John O’Brien came to St. John’s around 1818.  A dairy farmer, he built Thimble Cottage in the outskirts of the town. It still stands, although the family’s last descendant there, Aly O’Brien, passed away in 2008.  

O’Briens were also part of the Irish community in Antigonish county, Nova Scotia. The 1838 census listed O’Briens in Dorchester and Tracadie townships.:

  • Captain John O’Brien was a sea captain who based himself in Nova Scotia from the early 1800’s.  His son Joseph and grandsons William and John were also master mariners.  John ended up dying of yellow fever in the Caribbean in 1870.
  • Richard Baptist O”Brien, later a fervent advocate of Irish home rule, spent time as a priest in Antigonish county in the 1840’s.
  • while Michael J. O’Brien, the railway industrialist, was born at Lochaber in 1851. He and his son Ambrose were influential in the founding of the Montreal Canadiens and the National Hockey League.

New Zealand.  Six young O’Briens from Clare without education – four male and two female – came to New Zealand in stages between 1867 and 1880.  Two of them became policemen, one a gold-miner, and the fourth was a leader in the trade union movement.

Within a generation the family produced a lawyer, an All Black rugby player and a bank manager.  Later family members included a Rhodes Scholar and a prominent broadcaster.  There are about 25,000 descendants of this family around New Zealand today.  Their story was told in Kath Woodley’s 2011 book Bog Irish Micks – The O’Brien Family from Scariff.

O’Brien Surname Miscellany

O’Brien Early History.  The O’Brians emerged as chiefs of the Dalcassian tribe in SW Ireland which claimed a descent from the legendary Cormac Cas back in the 3rd century.   This claim may have been fanciful.   The Dalcassians in fact first began to appear in history in county Clare around the 8th century.

Their chief was crowned king of Thomond (or north Munster) two centuries later.  His son Mathgamain mac Cennetig was to expand their territory further, according to the Annals of Ulster, and he captured the Rock of Cashel (in present day Tipperary), thereby becoming the king of Cashel and Munster.

His younger brother Brian Boru, born around 940, first made himself king of Munster, then subjugated Leinster, and, eventually became the King of All Ireland, in the process ending the prior domination of the Ui Neills.  He died in 1014 in the celebrated battle of Clondorf when the Norsemen were finally defeated.  He was the founder of the O’Brien clan that was to follow.

The History of the O’Brien Clan.  The first O’Brien history, The Historical Memoir of the O’Briens, was written by John O’Donoghue and published in 1860.  It told the story of the O’Briens from Cormac Cas through Brian Boru and up until the end of the 18th century.

The author used as his source material the various reference works of Irish history that were available to him at the time, such as The Annals of the Four Masters, The Annals of Innisfallen, The Annals of Ulster, plus the works by John O’Donovan and other scholars of Irish history.  From these sources came the development of the O’Brien clan pedigrees.

The book, which has only been available in limited numbers, has recently been reprinted with a foreword by Morgan Llewelyn (who has written the story of Brian Boru) and portraits of the notable O’Briens in history.

There is an update on this O’Brien history which has taken the story to 1946.

The O’Briens at Comeragh Castle.  The first reference to the O’Briens of Comeragh castle, at the foot of the Comeragh mountains in Waterford, was in 1549 when Anthony O’Brien obtained a pardon from the English government.   However, they were never safe from the English.  The castle was besieged unsuccessfully in 1619.  During Cromwell’s time Derby O’Brien, the head of the O’Brien family at that time, was taken in 1656 and he died in captivity.

Then, after fierce resistance from the five sons of Derby O’Brien, Comeragh castle was captured by Cromwell.  He hanged four of these sons.  The fifth son, John of Kilnafrahane, managed to escape to the coast and he made a home for himself near Helvick Head.  From him came the O’Briens of Ballyetragh who were there through the 18th and 19th centuries.

Murrough O’Brien and His Son William, Earls of Inchiquin.  After Cromwell invaded Ireland in 1650, Murrough O’Brien left Ireland for France where he was to remain for ten years, scheming for the future King Charles II.

In 1660 he and his son William departed France for Portugal to help the Portuguese in their war with the Spanish.  However, both were captured by pirates in the Tagus.  William lost the sight of his left eye in the fight.  Murrough was ransomed.  And William was held as a captive hostage in Algiers for a year.

The O’Briens appear to have been rather lackadaisical commanders of their brigade in Portugal.  It was said that on the way to fight the Spanish, the Irish force hung around the coastal town of Peniche eating and drinking for weeks too long. “Um amigo de Peniche” came to mean a friend who has outstayed his welcome.

Around this time, with the restoration of Charles II, the Inchiquins were restored to favor in England.  Murrough returned to Ireland where he died in 1674.

A year later William was appointed the Governor of Tangier.  He was not a great success in this appointment as he was regarded as ineffectual and tactless and indeed was absent for two of the five years of his Governorship.  He was recalled to London to answer for his conduct in 1680.  Ten years later he was appointed the Governor of Jamaica, but again he was not a success. He died there after sixteen months in 1692.

Clare’s Dragoons.  Clare’s Dragoons, initially named O’Brien’s Regiment after its originator Daniel O’Brien the 3rd Viscount Clare, had been raised as a mounted dragoon regiment from Limerick to support the dethroned James II against the army of William or Orange in Ireland.

After the defeat at the Battle of the Boyne, the regiment reformed in France, first in 1689 and later in 1696. It fought under the name of Clare’s Dragoons in the service of France in various campaigns between 1696 and 1774.

Their marching song has survived.   The stanza which follows shows the O’Brien connection:

  • “Another Clare is here to lead,
  • The worthy son of such a breed
  • The French expect some famous deed,
  • When Clare leads on his bold dragoons.
  • Our colonel comes from Brian’s race,
  • His wounds are in his breast and face,
  • The bearna baoghil is still his place,
  • The foremost of his bold dragoon.
  • Viva la, the new brigade!
  • Viva la, the old one too!
  • Viva la, the rose shall fade
  • And the shamrock shine forever new!”

William Smith O’Brien, An Unlikely Rebel.  William Smith O’Brien, the son of Sir Lucius O’Brien, was born in 1803 at Dromoland castle in county Clare.  These O’Briens were one of the few families of Gaelic origin who had gained entrance to the Protestant landed elite.

He was educated at the great English public school of Harrow and then went on to Cambridge University.  He retained from his early associations an English accent which distanced him from his associates in Irish political life, one of whom described him as having ‘too much Smith and too little O’Brien.’

He sat in the British Parliament for twenty-one years, from 1828 to 1849. Although a Protestant country-gentleman, he supported Catholic Emancipation while remaining a supporter of British-Irish union.

However, disillusioned by the inadequacy of British government policies towards Ireland during the Famine years, his feelings began to change.  He associated himself with the radical Young Irelanders.  In July 1848 O’Brien and other Young Irelanders led a peasant rising against police at Ballingarry in Tipperary.  In O’Brien’s subsequent trial, the jury found him guilty of high treason and he was sentenced to transportation for life in Tasmania.

Early O’Briens in America.  Morris O’Brien had arrived in Machias, Maine from Cork in Ireland in 1765.  He was aged about fifty then and engaged himself in the lumber business, operating a sawmill with his sons.  He died in Machias in 1799 and his tombstone read:

“Here lie deposited the remains of Morris O’Brien, who died June 4, 1799, aged 84 years.

  • ‘Come think on me, as you pass by,
  • As you are now, I once was too;
  • As I am now so you must be,
  • Prepare for death to follow me.’”

He was an American patriot and the father of five sons, including Captain Jeremiah O’Brien, who all distinguished themselves during the Revolutionary War.

Some other early O’Brien arrivals in America can be seen in the table below.

Date O’Brien Vessel
1760’s Philip O’Bryan Russ Dublin to Maryland
1764 James and John Brien Hannah Cork to Boston
1766 Timothy Bryan Wilmott Cork to Boston
1767 Mary and Elizabeth O’Brien Ann
& Margaret
Ireland to Boston

Philip O’Bryan is believed to have come from Armagh.  He appeared on the census for Frederick county, Maryland in 1776 and served in the Maryland militia during the Revolutionary War.

The O’Briens and Thimble Cottage.  John O’Brien had come to Newfoundland from Ireland around 1818 and started his farm in fourteen acres of land that he had cleared in Freshwater valley near St. John’s.   He established a commercial dairy farm there and sold his milk to housewives and shopkeepers in the west end of St. John’s.

He had built two farmhouses on his land before he started work on a third one, on Nagle Hill in St. John’s, in 1850.  It was to be situated on a narrow, steep, winding gravel road on Nagle Hill, nestled in a forested grove and overlooking much of the city of St. John’s.

Built for his son Timothy, it took two winters to gather sufficient materials from the nearby forest to build the house. He made the chimney from locally-gathered stone and sheltered the structure with locally-made spruce shingles.  The two-and-a-half-storeyed salt-box house has a sloping roof which makes the structure a single storey at the rear where the kitchen is located.

The house is typical of a 19th century Newfoundland Irish farmhouse.  It is the sole survivor of approximately twenty similar homes that were once common in the Freshwater valley area.

Thimble Cottage survived the 1892 fires and has been continuously lived in by the O’Brien family since the time it was built.  In 1992 the Heritage Foundation of Newfoundland and Labrador rewarded the efforts of the O’Briens to preserve their land and home when Thimble Cottage was declared a Registered Heritage Structure.  Aly O’Brien who died there in 2008 was said to have been the last Gaelic speaker of Newfoundland.

O’Brien Names

  • Brian Boru, the legendary 10th century Irish king, left his name to the O’Brien clan.
  • Murrough O’Brien, known as Murcha of the Burnings, played a controversial role in mid 17th century Irish politics. He was made President of Munster for expelling the Catholics and then became a Catholic himself.
  • William Smith O’Brien from Clare was the 19th century Irish nationalist who led the 1848 Young Ireland uprising.
  • William O’Brien was the Irish nationalist who founded the United Irish League, the forerunner of Sinn Fein.
  • Edna O’Brien from Clare is an Irish novelist and short story writer who novels were first banned in Ireland.
  • Aidan O’Brien is a very successful Irish horserace trainer.
  • Conan O’Brien is an American comedian and late-night talk show host.

O’Brien Numbers Today

  • 37,000 in the UK (most numerous in Lancashire)
  • 60,000 in America (most numerous in New York)
  • 108,000 elsewhere (most numerous in Ireland)

O’Brien and Like Surnames 

The Irish clan or sept names come through the mists of time until they were found in Irish records such as The Annals of the Four Masters.  The names were Gaelic and this Gaelic order was preserved until it was battered down by the English in the 1600’s.

Some made peace with the English.  “Wild geese” fled to fight abroad.  But most stayed and suffered, losing land and even the use of their language.  Irish names became anglicized, although sometimes in a mishmash of spellings.  Mass emigration happened after the potato famine of the 1840’s.

Some surnames – such as Kelly, Murphy and O’Connor – span all parts of Ireland.  But most will have a territorial focus in one of the four Irish provinces – Leinster, Munster, Ulster, and Connacht.

Munster in SW Ireland covers the counties of Clare, Cork, Kerry, Limerick, Tipperary, and Waterford.  Here are some of the Munster surnames that you can check out.


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Written by Colin Shelley

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