He belonged to the northern race of Hy-Nial, being descended from Nial of the Nine Hostages.

On his death, the crown reverted to the southern Hy-Nials in the person of their representative, Tuathal Maelgarbh.
It would appear from a stanza in the Four Masters, that St.Brigid had some prophetic intimation or knowledge of one of the battles fought by Muircheartach.

Her name is scarcely less famous for miracles than that of the great apostle.

Broccan's Hymn[140] contains allusions to a very great number of these supernatural favours.

Many of these marvels are of a similar nature to those which the saints have been permitted to perform in all ages of the Church's history.
Brigid belonged to an illustrious family, who were lineally descended from Eochad, a brother of Conn of the Hundred Battles.