McGrath (Creagh, McCragh), Dermot (d. 1603?), catholic bishop of Cork and Cloyne, was born into a brehon family near Cahir, Co. Tipperary. In his youth he attended a bardic school at Cahir and a classical school at Clonmel before enrolling in the Germanic College in Rome, which had been founded for students from north European nations. Presumably he was ordained at Rome and may have received a doctorate of divinity there. He may also have taught or studied at Louvain and is said to have compiled a treatise on Christian doctrine, which was used as a textbook in Ireland. On 12 October 1580 he was appointed bishop of Cork and Cloyne and was consecrated in Rome by the year's end. On 3 April 1581 he was granted wide faculties as bishop, which was virtually a prerequisite if he was to achieve anything in what was essentially a missionary role in an area under English protestant governance. He travelled to Ireland via Spain, probably arriving in mid to late 1581.
Over the next two decades McGrath played a pivotal if rather obscure role in advancing counter-reformation catholicism in his own diocese and in Munster generally. Dressed usually in a simple peasant's garb, he seems to have been preoccupied mainly with ministering the sacraments to the catholic laity and with solidifying the widespread, but rather inchoate, support for catholicism in the province. Through his efforts, he acquired a great deal of influence in Munster and enjoyed the protection of powerful catholic lords, particularly the baron of Cahir. He was strongly anti-English and tried to encourage Spanish intervention in Ireland through his contacts in Madrid. Curiously, given his opposition to the government, the local officials appear to have made only half-hearted efforts to apprehend him, and generally ignored him completely, even though they intercepted his correspondence with Madrid in 1590 and were therefore aware of his activities. Indeed, both Miler Magrath (qv), Church of Ireland archbishop of Cashel and possibly a cousin of McGrath, and Sir John Perrot (qv), lord deputy of Ireland, were accused of colluding at his avoidance of capture. The crown's hold over Munster was still very tenuous, and it is possible that the local officials did not want to risk the popular backlash that would ensue if McGrath were arrested.
In the autumn of 1598, following the destruction by Hugh O'Neill (qv), earl of Tyrone, of a royal army at Yellow Ford, a number of leading Munster lords met at Holy Cross, Co. Tipperary, and at McGrath's prompting they pledged support for Tyrone's rebellion. However, the various rebel leaders were preoccupied mainly with advancing their own interests and the English believed it was only the efforts of McGrath, assisted by the Jesuit James Archer (qv), that held the Munster confederation together. When Tyrone marched into Munster in early 1600, McGrath accompanied him on his tour of the province. Tyrone produced a forged papal excommunication of those catholics who did not join the rebellion, which McGrath decided to accept after some hesitation. That spring McGrath used the forgery in an attempt to secure Lord Roche's and Viscount Buttevant's (qv) support for the rebellion. During this period Tyrone also appointed him to act as arbiter in a dispute between members of the MacCarthy Mór clan. By then, McGrath was of an advanced age and was increasingly infirm. On 31 March 1600 he wrote to Rome to say that he could no longer carry out his duties and asked the pope to fill the many vacant Irish bishoprics.
Following Tyrone's departure from Munster in 1600, he enjoyed the protection of James fitz Thomas Fitzgerald (qv), self-proclaimed earl of Desmond. However, under the energetic leadership of Sir George Carew (qv), the government re-established its control over much of Munster during 1600–01 and fitz Thomas and McGrath were soon hunted fugitives. Indeed, in December 1600 the bishop was very lucky to avoid capture, escaping only because Carew's soldiers did not recognise him. Fitz Thomas was eventually captured in May 1601, but McGrath continued to elude his pursuers.
During 1601, possibly due to illness and infirmity, he ceased to play a major role in events and, perhaps in recognition of this, government officials lost interest in his movements and in catching him. The last concrete reference to him occurs on 29 December 1601, when he excommunicated those catholics who fought against Tyrone's forces at the battle of Kinsale. Although some sources suggest that he lived for some years after 1603, he appears in fact to have died by May 1603.