The significance of Mac Carthaig's career lies in his command of territories in west Munster, at a time when the Tudor conquest of Ireland was underway.
In particular, he was accused of contact with William Stanley and Jacques de Franceschi, who had defected with a regiment of Irish soldiers from the English to the Spanish side in the Eighty Years' War in Flanders.
Initially detained by Carew at Shandon Castle in Cork,[1] after six months Mac Carthaig was moved to Dublin, and then to London, where he arrived in February 1589 to be committed to the Tower.
Mac Carthaig was examined by the privy council in March and denied all complicity in the continental intrigues of the English Catholic, Sir William Stanley.
He was sent back to the Tower, but fifteen months later his wife appeared at court and Sir Thomas Butler, 10th Earl of Ormonde, volunteered to stand surety for him in the sum of £1000.
However, the situation was transformed by the arrival in Munster of the Ulster forces of Hugh O'Neill, who was leading a nationwide rebellion – the Nine Years' War – against the English government in Ireland.
During the Nine Years' War in Munster, Mac Carthaig failed to engage with the English military campaign and secretly negotiated with the rebels under Hugh O'Neill and the Spanish.
O'Neill's strategy was to back those local Irish lords who had a grievance against English authority and were in command of sufficient land and followers to contribute to his war effort.
In April an English expedition led by Captain George Flower raided his lands in Carbery and fought a bloody skirmish with Mac Carthaig's levies, which left over 200 men dead between the two sides.
In fact, at this time Mac Carthaig, in an intercepted letter to Hugh Roe O'Donnell, had sought to assure the northern rebels of his commitment to their cause.
He was also the main contact in the south of Ireland for the Spanish, who planned a landing in Munster, which Mac Carthaig most likely expected would settle the war for good.
On 5 January 1600, he wrote to Philip II of Spain, via his agent in Ulster, Donagh mac Cormac Mac Carthaig, offering, his person and lands as well as his vassals and subjects to your Royal service…to receive favour and aid…seeing as there is no other that can and will assist us better against these Heretics in this holy enterprise.In the months that followed, Carew broke the rebellion in Munster, retaking rebel castles, arresting Fitzthomas, the Súgan Earl, and persuading Donal MacCarthy to change sides.
Having pacified the province, Carew had no intention of leaving Fínghin mac Donncha installed as MacCarthy Mór, judging that his supremacy would make any future English presence in the area impossible.
To this end, he arrested Florence, having called him to his camp for talks, 14 days before the expiry of the safe conduct "on discretion" (i.e. without charge) – an action which, although unlawful, was approved by the Queen's secretary, Robert Cecil, for reasons of state.
After the English victory at the battle of Kinsale, his brother, Diarmuid Maol ("Bald Dermot"), who commanded Fínghin mac Donncha's followers in his absence, was killed accidentally in a cattle-raid by some of Donal II O'Donovan's men under the command of Fínghin Mac Carthaig, his first cousin, son of his uncle Owen; many of his kinsmen were also killed in various encounters with English or rival Irish forces.
Then Sir Richard Boyle, Earl of Cork, and Lord Barry tried to wrest from Mac Carthaig the territory inherited from his father, but he successfully resisted by means of the law.
He went to the Marshalsea again in 1608, was released in 1614 on bonds of £5000 not to leave London, and in 1617 was recommitted to the Tower on the information of his servant, Teige O'Hurley, alleging his involvement with William Stanley and several exiled Irish Catholic priests and nobles, including Hugh Maguire.
Mac Carthaig was due for release in 1619 but was sent back to the Gatehouse in 1624, to "a little narrow close room without sight of the air", owing to the death of two of his sureties, Donogh O'Brien, 4th Earl of Thomond and Sir Patrick Barnewall.
Donagh MacCarthy, the son of Dermot Mac Carthaig, later created Viscount of Muskerry, would later be one of the leaders of the Irish Rebellion of 1641 and Confederate Ireland in the 1640s.