The O’Byrne Clan – A History

O’Byrne is one of the great names in Irish history. The O’Byrne Clan ruled from their strongholds in the Wicklow mountains for several centuries.

Here are some of the family names of O’Byrne ancestry. Are you amongst them?

  • Byrne, Burns, Beirne, Brin, Broin
  • O’Byrne, O’Burns, O’Brin, O’Broin

This article will tell you about the exploits of Fiach McHugh O’Byrne, the great mountain warrior. But before we get to Fiach McHugh, let’s start at the beginning this story.

We’ll start with the father of the man who gave his name to all O’Byrnes.

Mael Morda, Father Of Bran

Máel Morda’s tribe was from what’s now known as County Kildare in Leinster. He became a King of Leinster in the early years of the 11th century.

During that time, his future rival Brian Boru was rising in the south to become King of Munster. You can check out our article on Brian Boru, the ancestor of the O’Briens.

Brian set his sights on being High King of all Ireland, but many of the clans of Leinster refused to submit to his authority. Their loyalty was to Mael Morda.

Mael Morda and King Sitric of Dublin

Mael Morda struck an alliance with Sitric Silkenbeard, the Norse King of Dublin, and his Viking clans.

Sitric was the son of Mael Morda’s sister, Gormlaith. He called on his Norse allies in the Orkney Island and the Isle of Man to sail into Dublin.

Mael Morda and his allies met Brian Boru’s armies at the Battle Of Clontarf in 1014. Although Brian was victorious, he was killed at the end of the battle.

Mael Morda was killed in the battle by a nephew of Brian’s. His son Bran was recognized by the clans as the next King of Leinster.

Bran, King Of Leinster

Bran is also known as Braen, and took his name from the Gaelic word for a raven.

Bran’s reign as king of the province was relatively short-lived.

After Maelmorda was killed in 1014, his son Bran became King of Leinster, but he only ruled for four years.

His father’s old ally Sitric was his downfall. Sitric blinded Bran in 1018.

The significance of being blind was that the old Irish laws only allowed men who were physically “intact” to head a clan or be a king.

But Bran lived a long life. He eventually died in a monastery in Germany in 1052.

The O’Bryne Clan

The grandsons and later descendants of Bran called themselves “O’Bran”, meaning “descendant of Bran”.

This would be anglicized in later centuries as O’Byrne.

Their lands were in the north of what is now County Kildare. They were allied with the neighboring O’Tooles.

However, the Anglo-Norman invasion in the late 12th century eventually drove the O’Byrnes and the O’Tooles into the Wicklow mountains as refuge.

Both clans used the protection of the mountains to build their numbers and strength. For three centuries, they repelled attempts of conquest from the English power base in Dublin.

The O’Byrne’s Country

The O’Byrnes and the O’Tooles were the two most powerful clans south of Dublin.

The O’Byrne lands were known as “Crioch Branach”, or The O’Byrne’s Country. They ran from the northern tip of County Wicklow down to what is now Arklow town.

Downs Hill

The chiefs elected by the O’Byrne clan were given the title of “The O’Byrne”.

The chiefs were inaugurated on a tall hill that is now known as Downs Hill near the village of Delgany in County Wicklow.

If you go up to the top of Downs Hill now, your view will span most of The O’Byrne’s Country.

O’Byrne Septs

The Irish clans were made up of loyal families known as septs. The Septs would hold their own smaller territories.

The O’Byrnes of Ranelagh (Ranallach) were one of the most powerful of the O’Byrne septs. And perhaps the greatest Ranallach leader was Fiach McHugh O’Byrne.

The Battling O’Byrnes

When the Tudors took reign in England, they set out to bring the island of Ireland under the control of their monarchy.

Henry VIII and his daughter Elizabeth the First paid particular attention to Ireland. They already had control over Dublin. But they now spread their forces and demanded that the clans submit to their authority.

This led to splits within the O’Byrnes. Thady O’Byrne was The O’Byrne (the chief) in the 16th century who submitted to the crown.

However, the Sept of Ranelagh led by Hugh McShane O’Byrne refused to do the same.

When Hugh died, his son Fiach McHugh became leader of the Sept.

Fiach McHugh O’Byrne

Fiach’s name lives on in song and story as one of the great Irish warriors. You may also see his name spelled as Feagh.

He led his people for nearly twenty years into battle against English forces.

Fiach’s mountain base was at Glenmalure in the Wicklow mountains. He led several clans in skirmishes against the English forces out of Dublin. His forces also made raids into Dublin.

Battle of Glenmalure

Arthur Grey, an English Baron, sailed to Dublin in 1580 with reinforcements. He led an English army of 3,000 men down to Glenmalure to defeat the O’Byrnes.

As Grey’s soldiers climbed through the woods, they were ambushed. When they retreated in disarray, the Irish set upon them and cut them down with axes and swords.

Fiach and his victory are commemorated in a rousing (and bloody) marching song. You can find the lyrics and their meaning in our article on “Follow Me Up To Carlow”.

Playing cat-and-mouse with the crown

A year after his victory at the Battle of Glenmalure, Fiach agreed to terms with the crown and received a pardon.

The wily leader laid low for a while until he got involved with Red Hugh O’Donnell.

O’Donnell was a king in the Donegal region in the 1590s. He was captured by the English and held prisoner in Dublin Castle.

Red Hugh escaped in the winter of 1592 and fled south to the Wicklow mountains. Fiach McHugh took him in and gave him refuge. Once the Ulster king had recovered from frostbite, Fiach had him escorted safely back to his homelands.

Once again, English forces marched on O’Byrne who escaped their grasp. The princely sum of one hundred pounds was put on his head.

Fiach played a cat-and-mouse game of politics and alliances. He was eventually caught and executed in 1597.

The End Of The O’Byrne Chiefs

The defeat of allied Irish clans at the Battle Of Kinsale in 1601 led to the collapse of resistance to rule by the crown.

James I, the Stewart King, succeeded Elizabeth in 1603 and set out to suppress Gaelic traditions, laws, and language.

Part of this involved the destruction of the Clan systems and the end of the inauguration of clan Chiefs. Lands owned by clans were seized.

1578 saw the last inauguration of a Chief of the O’Byrne clan.

This doesn’t mean that O’Byrne families didn’t continue in alliance and resistance. You’ll find many O’Byrnes involved in the rebellions of 1641, 1689, and 1798. However, each was lost by the Irish sides.


The loss of the 1689 rebellion saw many O’Byrnes going to France and other parts of continental Europe. They served in armies loyal to Catholic kings.

These Irish soldiers are often referred to as the Wild Geese.

The loss of the 1798 rebellion saw many O’Byrns depart for Australia.

However, it was the Great Famine of the 1840s that saw an exodus of Irish people to the United States. Many O’Byrnes were amongst those numbers. You can learn more in our article on how common a surname Byrne is in Ireland and America.