Ua hEochada, Donnchad (d. 1113), son of Donn Slébe and overking of Ulaid, belonged to the dynasty of Dál Fiatach. For most of the eleventh century, the dynasty had been wracked by internal dissensions; since the death of the eponymous Eochaid (1004), the kingship had been contested by representatives of different family lines, including that of Ua Mathgamna. Donnchad's father, Donn Slébe son of Eochaid, was overking of Ulaid from 1071 to 1091, but was twice displaced by rivals. His mother was Órlaith of the Uí Chnáimíne, a minor lineage of Dál Cais. He had four half-brothers: Eochaid (known as Goll Garbraige), Conchobar, Áed, and Niall. There is no record of Donnchad's own marriage, but he had at least one son (fl. c.1101) who is not further identified.
Donnchad succeeded to the kingship in 1091 when his father was slain by the Cenél nÉogain king of Ailech, Domnall Ua Lochlainn (qv), at the battle of Belach Goirt (Co. Armagh). He remained a significant figure in regional politics for twenty-two years, although his reign was interrupted at two stages by his brother Goll Garbraige. After a rígdál (royal meeting) near Lough Neagh in 1093, Donnchad was pressed into an alliance with Domnall Ua Lochlainn and took part in an offensive against the Dál Cais overking of Munster, Muirchertach Ua Briain (qv). It seems that he was uneasy about this arrangement, perhaps because of his mother's connections. Although the allies achieved a minor military success in Co. Kildare, the Ulaid abandoned the offensive and returned home, causing the northern forces to lose the initiative. Thereafter, it seems that the powerful king of Ailech distrusted him; as his reign progressed he came increasingly under pressure from that quarter. Striving to suppress opposition among his sub-kings, in 1094 he blinded the local ruler of Uí Echdach (in Co. Down).
Donnchad appears, however, to have overlooked or to have been unable to deal with contention within his own family; when defeated in battle (1095) by the neighbouring dynasty of Dál nAraide, he was deposed by his brother Goll Garbraige. He did not regain the kingship till 1099. That same year Ulaid was invaded by Domnall Ua Lochlainn; after defeat in a cavalry skirmish, the traditional Dál Fiatach inauguration site at Cráeb Tulcha (Crew Hill, parish of Glenavy, Co. Antrim) was levelled. On 28 May 1100 Donnchad suffered the further humiliation of being captured with a party of his nobles by the Cenél nÉogain. He was held for eighteen months till Domnall (qv), abbot of Armagh, intervened ‘for the sake of his son and fosterling’. He was released in the great church of Armagh on 22 Dec 1101. During his absence, Goll Garbraige had again taken the kingship, and apparently retained it for eight years.
In this period the powerful king of Ailech exerted renewed pressure on Dál Fiatach. An incursion into Mag Coba (1102) led to two Cenél nÉogain dynasts being slain by the Ulaid in a night-raid. The following year, another hosting to Mag Coba by Cenél nÉogain prompted Muirchertach Ua Briain to intervene – with disastrous results for the men of Munster. Attempts by Donnchad's brothers to subdue their immediate neigbours were equally unsuccessful; they were defeated by Dál nAraide in 1104, and Conchobar was slain in 1107 on an incursion into Fernmag (barony of Farney, Co. Monaghan). Donnchad's chance to retake the kingship came in 1108, when Goll Garbraige was slain by men of the rival Ua Mathgamna line. He still faced pressure from Ailech, and his obligation to yield hostages in 1109 clearly rankled. In 1111 he raided the heartland of Cenél nÉogain, and destroyed their traditional inauguration site at Telach Óc (Tullaghogue, Co. Tyrone). This led to a retaliatory cattle raid in which he suffered considerable losses. He made peace with Domnall Ua Lochlainn, and rendered hostages and tribute.
Presumably, Ua Lochlainn was less than satisfied with Donnchad's guarantees. In a seemingly unprovoked invasion (1113), Donnchad was driven from power and the overkingship of Ulaid was partitioned: the king of Ailech brought Dál nAraide under his own control and divided Dál Fiatach between Donnchad's surviving brothers and Eochaid Ua Mathgamna. Despite the intervention of Ua Briain and of Cellach (qv), bishop of Armagh, conflict within Dál Fiatach escalated. Donnchad was blinded by Ua Mathgamna, and the kingship remained weak and divided till his nephew, Cú Ulad son of Conchobar (king 1131–57) managed to restore stability.