His father, Eochada mac Ardgair, died in 1004. His early military ventures were against members of his own sept, Dál Fiatach. He defeated a cousin in 1012 at the ‘battle of the Summits’ and in 1020 defeated and blinded Flaithbertach Ua Eochada.[1]
In 1022 he defeated the Dublin Norse at sea.[2] He then defeated the Cenél nEógain client kingdom of Airgialla. In 1024 he invaded Dublin and took hostages; a success he repeated two years later.[1]
In 1044 mac Eochada raided the southern Uí Néill kingdom of Brega, but was defeated, losing 200 men.[1]
In 1047 he made an alliance with Diarmait mac Maíl na mBó which helped to put pressure, from both north and south, on the kingdoms of Mide, Brega and Dublin [3]
In 1056 the southern Uí Néill took 3,000 cows and 60 captives from his client Kingdom Dál nAraidi which was also raided by the Cenél nEógain in 1059.[1]
Niall's son Eochaid (died 1062) was considered co-king of Ulaid with his father. Eochaid's son Donn Sléibe Ua hEochada (died 1091) was also a king of Ulaid, as were many of his descendants.[4]
