He was descended from Dá Slúaig, the son of Ainmere so he was a member of the Húi Nadsluaga clan who were one of the five prímthúatha of Dál mBuinne, east of Lough Neagh, County Antrim.
This was mainly due to his influence over two successive High Kings of Ireland, Áed Allán whose spiritual confessor he was and Flaithbertach mac Loingsig whose bishop-abbot he was.
Before the reign of Congus the primates generally restricted themselves to the see of Armagh but afterwards they began to make circuits and visitations through the rest of Ireland for the collection of their dues.
Geoffrey Keating states- "It was about this time that a meeting took place between Aodh Ollan, king of Ireland, and Cathal, son of Fionghaine, king of Munster, at Tir Daghlas, in Urmhumha, where they imposed Patrick's rule and law and tribute on Ireland" The Annals of Ulster have the following entries under the year 737- "A meeting between Aed Allán and Cathal at Tír dá Glas.
The law of Patrick was in force in Ireland" A further impetus to the widening influence of Armagh was the fact that the High King of Ireland Flaithbertach mac Loingsig of the Cenél Conaill abdicated his throne in 734 and went to reside in Armagh monastery for the rest of his life The Battle of Fochart in 732 is alleged to have taken place between Áed Róin, king of Ulaid, and Áed Allán, High King of Ireland, as a result of a quatrain composed by Congus whilst bishop.