[1][2] In the course of a quarrel with his father and his half-brother Hugh, Calvagh sought aid in Scotland from the Campbells, who with access to Scottish royal artillery were able to assist him in deposing Manus and securing the now very divided lordship of Tyrconnell for himself.

Shane accordingly invaded Tyrconnell at the head of a large army in 1557, desiring to make himself supreme throughout Ulster, and encamped on the shore of Lough Swilly.

[9] Calvagh was then recognized by the English government as lord of Tyrconnell;[10] but in 1561 he and his wife were kidnapped by Shane O'Neill in the Franciscan friary of Killydonnell.

[3] On 26 October, in the midst of his cavalry, Calvagh suddenly fell dead from his horse on the public road between Baile-aghaidh-chaoin and the church of Rath.

[11][2] As his son Conn was a prisoner in the hands of Shane O'Neill, his half-brother Hugh MacManus was inaugurated The O'Donnell in his place.