In the early centuries CE, Munster is the domain of the Iverni and the legendary Clanna Dedad led by Cú Roí and to whom the celebrated Conaire Mór also belongs.

During the Early Middle Ages, most of the area is part of the Kingdom of Munster, ruled by the Eóganachta dynasty, who succeed the once mighty Dáirine and Corcu Loígde overlords from the early 7th century onwards, perhaps beginning with the notable career of Faílbe Flann mac Áedo Duib.

Later rulers from the Eóganachta who will dominate a greater part of Ireland are Cathal mac Finguine and Feidlimid mac Cremthanin.

Notable regional kingdoms and lordships of Early Medieval Munster are Iarmuman (West Munster), Osraige (Ossory), Uí Liatháin, Uí Fidgenti, Éile, Múscraige, Ciarraige Luachra, Corcu Duibne, Corcu Baiscinn, and Déisi Muman.

By the 9th century, the Gaels have been joined by Norse Vikings who founds towns such as Cork, Waterford and Limerick, for the most part incorporated into a maritime empire by the Dynasty of Ivar, who periodically will threaten Munster with conquest in the next century.

Around this period Ossory breaks away from Munster.

The 10th century century ses the rise of the Dalcassians (probably descendants of the ancient Mairtine, a sept of the Iverni/Érainn), who had earlier annexed Thomond, north of the Shannon to Munster.

Their leaders are the ancestors of the O'Brien dynasty and spawn Brian Bóruma, perhaps the most noted High King of Ireland, and several of whose descendants are also High Kings.

By 1118, Munster has fractured into the Kingdom of Thomond under the O'Briens, the Kingdom of Desmond under the MacCarthy dynasty (Eóganachta), and the short-lived Kingdom of Ormond under the O'Kennedys (another Dalcassian sept).