Cathal mac Finguine (died 742) was an Irish King of Munster or Cashel, and effectively High King of Ireland as well. He belonged to the Eóganacht Glendamnach sept of the dominant Eóganachta kin-group whose members dominated Munster from the 7th century to the 10th. His father, uncle, grandfather and great-grandfather had also been kings of Cashel, as were his son and grandson.

Cathal's conflict with the Uí Néill kings, Fergal mac Máele Dúin, Flaithbertach mac Loingsig, and Áed Allán, son of Fergal mac Máele Dúin, is reported at some length in the Irish annals, and again northern and southern versions provide differing accounts. Cathal also appears as a character, not always portrayed sympathetically as in Aislinge Meic Con Glinne where he is possessed by a demon of gluttony, in a number of prose and verse tales in the Middle Irish language.

Widely regarded as the most powerful Irish king of the first half of the 8th century, and the strongest (historical) king from Munster before Brian Bóruma, Cathal mac Finguine is believed to be the last king mentioned in the Baile Chuinn Chétchathaig. The most expansionist historical Eóganacht king before him was Faílbe Flann mac Áedo Duib (d. 639).

The Eóganachta kingship, which had its chief seat at Cashel and chief church at Emly, was the most powerful in the southern half of Ireland, while the various branches of the Uí Néill and Connachta dominated the northern half. At this time, the Uí Néill were striving to be the sole Kings of Tara, with the succession generally alternating between the northern and southern branches of the Uí Néill, although the ancient ceremonial kingship had not long before been held by the Laigin and Ulaid, and more distantly the Dáirine and Érainn. The kingship of Cashel, argued in early Munster sources, e.g., the Uraicecht Becc, as actually the most powerful in Ireland, was founded in the middle of the 5th century by the descendants of Conall Corc and Aimend, the "inner circle" of the Eóganachta, who after a century and a half of able politicking had come to supersede the overlordship of the Corcu Loígde in Munster.

For the century and a quarter until Cathal's death, the kingship of Cashel was dominated by the Eóganacht Chaisil and Eóganacht Glendamnach septs of the inner circle. The lands of the Glendamnach lay to the south-west of Cashel, in the middle valley of the Blackwater. Cathal's father, Finguine mac Cathail Con-cen-máthair (d. 696), uncle, Ailill mac Cathail (d. 701), grandfather, Cathal Cú-cen-máthair (d. 665/666), and great-grandfather, Cathal mac Áedo (d. 628), had been kings of Cashel.

Cathal's immediate predecessor was probably Cormac mac Ailello of the Caisil sept, who was killed in battle against the Déisi in 713. Eterscél mac Máele Umai, who had been king and did not die until 721, had probably abdicated much earlier so that Cathal was king at Cashel from around 713 onwards.

While the Uí Néill and Eóganachta were the most important kingships in Ireland, the kings of Leinster and the kings of Connacht were significant forces. Leinster, once a much larger region, the northern parts of which had been conquered by the Uí Néill, was the target of expansionist Uí Néill kings, and also of the Eóganachta. The contest for control of Leinster would play a major part in Cathal's reign, and indeed in relations between the Eóganachta and Uí Néill in the centuries which followed. The kings of Connacht claimed a common kinship with the Uí Néill, and were largely favourable towards them. The remaining provincial kingship, that of the kings of Ulster, controlled a much smaller area than the later province of Ulster, largely confined to the lands north and east of Lough Neagh, and was generally hostile to the Uí Néill. Finally, in the vast province of Munster itself there were several respectable but peripheral dynasties, such as the Uí Liatháin (for whom see below), whose relationships with the Eóganachta were rather distant and ambiguous.

The earliest record concerning Cathal, although it does not explicitly name him, is in 715 when Murchad mac Brain Mut of the Uí Dúnlainge, the king of Leinster, led his inaugural raid against Cashel. The first event to mention Cathal is in 721 when he and Murchad mac Brain attacked the lands of the southern Uí Néill. The Annals of Ulster report: "[t]he wasting of Mag Breg by Cathal son of Finnguine, and by Murchad son of Bran." Later that year, Fergal mac Máele Dúin retaliated, not against Cathal and Munster, but against Murchad and Leinster. The Annals of Ulster report: "An invasion of the Laigin by Fergal, and the cattle tribute was imposed and the hostages of the Laigin secured for Fergal son of Mael Dúin." That Fergal attacked Leinster in retaliation for the raid on Brega may mean that Cathal was, as Irwin notes, "the junior partner".