The high kingship of Ireland rotated between the Cenél nEógain and Cenél Conaill branches in the late 6th century. Eochaid ruled jointly with his uncle Báetán mac Muirchertaig (died 572) from 569. The middle Irish king lists have misplaced their reign putting it earlier than the annalistic tradition but other king lists have them in the correct order. They are also omitted from the earliest list of Kings of Tara, the Baile Chuind (The Ecstasy of Conn), a late 7th-century Irish poem. It is possible that the Ulaid king, Báetán mac Cairill (died 581), was the actual high king at this time.
In 572 the two kings were defeated and slain by Crónán mac Tigernaig, king of the Ciannachta of Glenn Geimin (Glengiven in modern County Londonderry).