Cennétig (d. 951), son of Lorcán and overking of north Munster, was the first representative of the Dál Cais dynasty to achieve prominence at national level. He belonged to the lineage of Uí Thairdelbaig, which in the early tenth century was contesting the kingship of Dál Cais (east Co. Clare) with the rival segment of Uí Óengusso. It appears that Cennétig's father, Lorcán son of Lachtna, earlier reigned as king, although his exact chronology remains uncertain. Cennétig's immediate predecessor, however, was probably the obscure Rebachán son of Mothla, who died (934) as abbot of Tuamgraney and king of Dál Cais. Cennétig was married to Bébinn, daughter of Aurchad son of Murchad, king of Iar-Chonnachta (western Connacht). He may well have had more than one wife, as he is credited with twelve sons, ten of whom are named; these included Echtigern, Donn-cuan, Lachtna, the more distinguished Mathgamain (qv), Brian Bórama (qv), and Marcán, abbot of Tuamgraney (d. 1010); in addition, he had at least one daughter, Órlaith.
The years from c.934 onwards witnessed the consolidation of Cennétig's lineage not only within the local kingship of Dál Cais but within Tuathmumu (Thomond; north Munster). While it remains possible that the still powerful Uí Néill lineage of Clann Cholmáin played some part in promoting Cennétig and his dynasty as a counter-balance to the Éoganachta, it is important not to overstate this connection. Other factors in the equation would include political fragmentation within the Éoganacht dynasties in the tenth century, and the potential to exploit the multiplicity of minor ruling lines in the basin of the lower Shannon. Nonetheless, Cennétig's daughter Órlaith was married to the king of Tara, Donnchad Donn (qv) son of Flann Sinna (qv). The latter's apparent willingness to execute her for adultery (941) may point to a marriage of convenience with a minor dynasty, the continued support of which was not crucial to Donnchad. The capture of Cellachán Caisil (qv), Éoganacht overking of Munster, that same year opened up an opportunity for Cennétig. Notwithstanding an admission by the twelfth-century tract ‘Caithréim Cellacháin’ that a share in the provincial kingship had been conceded to Cennétig, the probability is that the latter revolted against his overlords. In that event, Cennétig's aspirations were overturned by Cellachán at the battle of Gort Rottacháin (944); references to an encounter at Mag Dúin may relate to the same defeat. Cennétig lost two of his sons in this revolt, although the personal names assigned to them in the record, Dub and Finn, appear contrived.
In spite of this defeat, it seems that Cennétig continued to strengthen his position. When Congalach Cnogba (qv) son of Máel-mithig became established as king of Tara he invaded north Munster, probably because he considered that Cennétig posed a threat. As a result two more of Cennétig's sons, Echtigern and Donn-cuan, were slain. Cennétig himself, significantly styled rígdamna Caisil (eligible for the kingship of Munster) in the Annals of Ulster, died in 951; according to the ‘Cogadh Gáedhel re Gallaibh’ (§37) he was slain. His son Lachtna followed him in the kingship. The latter was slain two years later in an internal conflict, but two more of Cennétig's sons, Mathgamain and his even more illustrious brother Brian Bórama, in turn enjoyed distinguished reigns.