Congal Cennmagair (died 710) was High King of Ireland. He belonged to the northern Cenél Conaill branch of the Uí Néill. His father, Fergus Fanát, was not a high king, although his grandfather, Domnall mac Áedo (died 642), was counted as a High King of Ireland.
Congal was a guarantor of Adomnán's "law of the innocents"—the Cáin Adomnáin—agreed at the Synod of Birr in 697. He is the second lay guarantor listed after Loingsech and is called King of Tyrconell, though these titles may have been added later.
The reigns of Loingsech and Congal represented the peak of Cenél Conaill, thereafter eclipsed by the rival kinsmen the Cenél nEógain. Both appear to have attempted to expand into Connacht, with mixed results. Loingsech died in the pursuit of this goal, while in Congal's reign a notable victory was won against the men of Connacht in 707 and the Connacht king Indrechtach mac Dúnchado was slain. Congal himself did not participate in this battle but Loingsech's son Fergal did.
In the same year Congal himself campaigned in Leinster. Geoffrey Keating's Foras Feasa ar Éirinn records that he burned the church of Kildare during this and implies his death was related to this.
Congal himself died suddenly in 710. A gloss to the Annals of Ulster adds that this was due to a fit. Congal left a number of sons, none of whom was especially prominent. These sons included Flann Gohan (died 732) and Conaing (died 733) who were slain in warfare between Cenél Conaill and Cenél nEógain and a son named Donngal (died 731). He was followed as High King by another northerner, Fergal mac Máele Dúin (died 722) of the Cenél nEógain.
- After Seán Duffy (ed.), Atlas of Irish History, pp. 18–19.
- Francis J.Byrne, Irish Kings and High-Kings, Table 4
- the Laud Synchronisms give him a reign of 6 years while the Book of Leinster and Rawlinson Genealogies give him 8 years
- T.M. Charles-Edwards, Early Christian Ireland, pg.539
- Annals of Ulster AU 707.2
- Annals of Ulster AU 707.7
- Geoffrey Keating. History of Ireland, Book II, pg.143
- Annals of Ulster AU 710.3
- Annals of Ulster, AU 732.10, 733.3
- Annals of Ulster at CELT: Corpus of Electronic Texts at University College Cork
- Byrne, Francis John (1973), Irish Kings and High-Kings, London: Batsford, ISBN 0-7134-5882-8
- Charles-Edwards, T. M. (2000), Early Christian Ireland, Cambridge: Cambridge University Press, ISBN 0-521-36395-0
- Doherty, Charles (2004), "Congal Cennmagair (d. 710)", Oxford Dictionary of National Biography, Oxford University Press, retrieved 2007-10-22
- Geoffrey Keating, History of Ireland at CELT: Corpus of Electronic Texts at University College Cork
- Meyer, Kuno (1905), Cain Adamnain: An Old-Irish Treatise on the Law of Adamnan, Oxford: Clarendon Press, retrieved 2008-03-23