Congalach is one of the twelve "kings of Ireland" listed in the hand of the original scribe of the Annals of Ulster.
[2] Maternally, Congalach was a member of Clann Cholmáin, the dominant branch of the southern Uí Néill, a grandson of Flann Sinna and sister's son of his predecessor as High King Donnchad Donn.
[3] The Annals of Innisfallen, rather than having Congalach as sole High King, associate him with his frequent enemy Ruaidrí ua Canannáin of the Cenél Conaill.
[4] The Irish annals record Congalach at war with most of his neighbours, variously ally and enemy of the Norse-Gael king of Dublin Amlaíb Cuarán.
Congalach eventually met his death fighting the Laigin and the Norse-Gaels of Dublin in 956, in an ambush at Dún Ailinne (County Kildare).