The Uí Chernaig were styled kings of Lagore, or of south Brega, named after Loch Gabhair in modern County Meath.
During Tigernach's reign the Irish midlands were dominated by his distant Uí Néill kinsman, the High King Máel Sechnaill mac Máele Ruanaid of Clann Cholmáin.
In 848, probably as part of a broad alliance of Irish kings, Tigernach gained a victory over Vikings at Dísert Do-Chonna, an unidentified location, probably near the coast in the east midlands of Ireland.
Cináed, who became king of north Brega in 849, allied with Vikings in 850 and, according to the Annals of Ulster, "plundered the Uí Néill from the Shannon to the sea".
His obituary calls Tigernach king of Lagore (rí Locha Gabor) and co-king of Brega (lethrí Breg).