He travelled abroad, and on his return in 1634 went to court, next year marrying Katherine Manners, widow of the 1st duke of Buckingham, and living on her fortune for some years in great splendour. In 1639, on the outbreak of the Scottish war, he initiated a scheme of raising a force in Ireland to attack Argyll in Scotland and recover Kintyre (or Cantire), a district formerly possessed by his family; but the plan, discouraged and ridiculed by Strafford, miscarried (Strafford's Letters, ii. 300).
Soon afterwards he returned to Ireland, and sought in 1641 to create a diversion, together with Ormonde, for Charles I against the parliament. He joined in his schemes Lord Slane and Sir Phelim O'Neill, later leaders of the rebellion, but on the outbreak of the Irish Rebellion of 1641 in the autumn he dissociated himself from his allies and retired to his castle at Dunluce (now in Northern Ireland).
His suspicious conduct, however, and his Roman Catholicism, caused him to be regarded as an enemy by the English party. In May 1642 he was captured at Dunluce Castle by the Scottish Covenanter general Robert Monro, and imprisoned at Carrickfergus. Escaping thence he joined the queen at York; and subsequently, having proceeded to Ireland to negotiate a cessation of hostilities between the English Royalists and Irish Catholic rebels, he was again captured with his papers in May 1643 and confined at Carrickfergus, thence once more escaping and making his way to Kilkenny, the headquarters of the Roman Catholic confederation.
He returned to Oxford in December with a scheme for raising 10,000 Irish for service in England and 2000 to join Montrose in Scotland, which through the influence of the duchess of Buckingham secured the consent of the king. On January 26, 1644 Antrim was created a marquess. He returned to Kilkenny in February, took the Irish Confederate oath of association, and was made a member of the council and lieutenant-general of the forces of the Catholic confederacy. The confederacy, however, giving him no support in his projects, he threw up his commission, and with Ormonde's help despatched about 1600 men under his kinsman Alasdair MacColla in June to Montrose's assistance in Scotland, sparking a Scottish civil war. Antrim subsequently returned to Oxford and being sent by the king in 1645 with letters for the queen at Saint-Germain-en-Laye.
He proceeded thence to Flanders and fitted out two frigates with military stores, which he brought to the Prince of Wales at Falmouth. He visited Cork and afterwards in July 1646 joined his troops in Scotland, with the hope of expelling Argyll from Kintyre; but he was obliged to retire by order of the king, and returning to Ireland threw himself into the intrigues between the various factions.
In 1647 he was appointed with two others by the Irish confederacy to negotiate a treaty with the Prince of Wales in France, and though he anticipated his companions by starting a week before them, he failed to secure the coveted lord-lieutenancy, which was confirmed to Ormonde. He now ceased to support the Roman Catholics or the king's cause; opposed the treaty between Ormonde, and the confederates; supported the project of union between O'Neill and the parliament; and in 1649 entered into communications with Cromwell, for whom he performed various services during the Cromwellian conquest of Ireland, though there appears no authority to support Carte's story that Antrim was the author of a forged agreement for the betrayal of the king's army by Lord Inchiquin (Life of Ormonde, iii. 509; see also Cal. of State Papers, Ireland, 1660-1662, pp. 294, 217; Cal. of Clarendon St. Pap., ii. 69, and Gardiner's Commonwealth, i. 153). Subsequently he joined Ireton, and was present at the siege of Carlow.
He returned to England in December 1650, and in lieu of his confiscated estate received a pension of £500 and later of £800, together with lands in County Mayo. At the Restoration Antrim was excluded from the Act of Oblivion on account of his religion, and on presenting himself at court was imprisoned in the Tower, subsequently being called before the lords justices in Ireland, In 1663 he succeeded, in spite of Ormonde's opposition, in securing a decree of innocence from the commissioners of claims. This raised an outcry from the adventurers who had been put in possession of his lands, and who procured a fresh trial; but Antrim appealed to the king, and through the influence of the queen mother obtained a pardon, his estates being restored to him by the Irish, Act of Explanation in 1665 (Hallam, Const. Hist., iii. 396 (ed. 1855)).
Antrim is described by Clarendon as "of handsome appearance but of excessive pride and vanity and of a marvellous weak and narrow understanding." He married secondly Rose, daughter of Sir Henry O'Neill, but had no children, being succeeded in the earldom by his brother Alexander, 3rd earl of Antrim.
NIMBA Notebook: BUSY TIME FOR THE BUTCHERS; Northern Ireland Master Butchers' Association Member, HARRY MARQUESS, of Antrim, Reports on a Barbeque Boom
Jun 23, 2001; Byline: HARRY MARQUESS WE 21st century butchers prepare products unheard of even a decade ago as this ancient trade changes to...