Ruaidrí was not a favourite of his father, his brother Conchobar Ua Conchobair being Tairrdelbach's tánaiste and designated heir.

Aedh was blinded by Conchobar on Tairrdelbach's orders but Ruaidrí was protected by the Archbishop of Connacht, Muireadhach Ua Dubhthaigh.

Donnell Mór Mideach began to lose favour in 1147 and his fate was sealed when he was arrested in 1151, making solid Ruadrí's claim as his father's heir.

In that year, Ruadrí successfully raided Thomond, where Tairrdelbach won a great victory at the Battle of Móin Mór.

[citation needed] Ruaidrí remained active in suppressing the Ua Briains of Munster, burning Croome, dividing Munster in half (Thomond to Tadhg Ua Briain, Desmond to Diarmaid MacCartaigh), expelling Toirrdelbach mac Diarmata into Ailech.

[8] The Ua Conchobairs brought "the fleets of Dun-Gaillmhe, of Conmhaicne-mara, of the men of Umhall, of Ui-Amhalghadha, and Ui-Fiachrach" north and defeated Mac Lochlainn at Inis Eoghain, but the latter was strong on land, forcing them to respond to incursions in east Connacht and Breifne, along with attempted settlements in Mide in 1155.

On learning of Tairrdelbach's death, Mac Lochlainn assumed the High Kingship and began a war of attrition in Leinster and Osraige, using their regional allies against one another.

Forced to attack or lose face, Ruaidrí responded by plundering and burning areas around Strabane and Derry.

[citation needed] After the death of Mac Lochlainn in 1166, Ruadhrí rode to Dublin where he was inaugurated as High King of Ireland, arguably the first without opposition.

Ruadhrí experienced mixed success fighting the Norman and their rebellious Irish allies, losing much of Leinster, along with the Norse-Gael cities of Waterford and Wexford.

However, the King was defeated after the Normans sallied out to Ruadhrí's camp and killed many of the Irish soldiers as they were resting and bathing.

[11] This army was part of a massive counter-offensive led by the High King which pushed the Normans out of the Midlands and towards Dublin and the east coast.

[13][11] The last of Ruaidrí's descendants to hold the kingship of Connacht, Aedh mac Ruaidri Ua Conchobair, died in 1233.

The Ó Conchubhair Donn, the senior member of the entire Síol Muireadaigh dynasty, likewise descends from Cathal Crobhdearg.