He ruled as king of the Cenél Loairn from around 698 until his abdication in 723, but it may be that he was undisputed ruler of Dál Riata only in the final years of his reign.
Although Selbach is first mentioned after the death of Fiannamail ua Dúnchado (died 700), it seems likely that he had deposed his brother Ainbcellach in 698.
In 701 he destroyed Dún Olaigh, but whether this was in a war against Ainbcellach, against a king of the rival Cenél nGabráin, or some other enemies, is unknown.
In 712 Selbach besieged Aberte (Dunaverty, near Southend, Kintyre, in the lands of the Cenél nGabráin) and rebuilt Dún Olaigh in 714.
In 723 Selbach abdicated and retired to a monastery, at which time one annalist calls him lord of Dál Riada.