[1] He succeeded his nephew Muiredach Muillethan mac Fergusso (died 702) as king in 702.
To confuse matters further he is listed as the guarantor of the Cáin Adomnáin in 697 at the Synod of Birr as King of Connacht.
In July, 703 the high-king Loingsech mac Óengusso of the Cenél Conaill led a large army into Connacht to levy tribute but was defeated and slain along with many of his sons and other kings of the Ui Neill at the Battle of Corann (in South County Sligo).
The reason for Loingsech's attack may have been because the Cenél nEógain had outflanked the Cenél Conaill in the north resulting in expansion into Connacht as the only option available for them as well as a desire by Loingsech to assert his authority as high king.
At his death obit in 705 in the annals it is mentioned that he entered the clerical life.