Dillon was the grandson of an Irish Catholic officer in the French service and son of a convert absentee with a substantial Irish estate who lived on his Oxfordshire one and whose chief ambition was an English peerage. He was brought up by his childless uncle, Lord Mulgrave, as if he had been his own son.
On the eve of the election of 1802, he came to terms with one of the sitting Members Colonel Jackson, whose withdrawal secured Dillon’s unopposed return. Government had refused to arrange this for the Dillons and, as county Member, he was regarded as unfriendly to them.
On Pitt’s return to power Dillon was at first listed a Grenvillite, but acted as teller for the Irish duties, 22 June 1804, and could be counted by the autumn a friend of government, as also in December. On 15 Jan. 1805 he moved the address to Pitt’s satisfaction, congratulating ministers on the war effort. His honeymoon with government ended abruptly when he supported and was teller for the Catholic petition, 14 May 1805, announcing that Pitt’s resistance to Catholic claims prevented him from supporting the minister any longer. He again wrote a pamphlet on the subject.
Dillon voted against the Grenville ministry over Ellenborough’s seat in the cabinet, 3 Mar. 1806, and could not have been satisfied with Fox’s evasive answer to his question in the House as to the prospects for Catholic claims, 11 Mar. In May he was listed as not supporting ministers ‘at present’. After the election, he was still regarded as hostile, though given the command of a regiment raised by his father and accepted by government. He was absent in April 1807 from the discussion of the dismissal of ministers over the Catholic question. Yet the Portland ministry regarded him as hostile to them; and rightly so, for he voted with opposition on the address and Whitbread’s state of the nation motion, 26 June and 6 July 1807, seconded Lord Cochrane’s motion of 10 July, deplored the Irish tithe system, 15 July, and was also hostile in debate on the Irish questions of 4, 7 and 13 Aug. Lord Sligo now described him as ‘bottle washer to Sir Francis Burdett’.
In the Parliament of 1812 he voted in support of Burdett’s Regency motion, 23 Feb. 1813, and of Catholic relief, 2 Mar., 13 and 24 May 1813, before succeeding to his father’s title in November. Latterly he lived in Italy in financial distress, but was characterized as ‘a complete master of Irish politics’. He was evidently ‘a gentlemanly man, handsome, a great talker’, who never allowed his interlocutor to get in a word edgeways. Dillon, who also wrote A discourse upon the theory of legitimate government (1817), a Commentary on the policy of nations, a Commentary on the military establishments and defence of the British Empire (1812) and published an edition of Aelian’s Tactics (1814), as well as novels and poetry, died 24 July 1832.
