Trench was first returned to the Irish parliament in 1796 by his wife’s uncle Thomas Conolly. A year later he succeeded his father, who had held the seat for nearly 30 years, in the representation of county Galway. He opposed the Union in 1799 but was induced by Castlereagh, who thought him ‘very intelligent’ and became his friend for life, to change his mind. His father became a viscount on the occasion and his brother a bishop. He was duly listed a ‘respectable’ supporter of government at Westminster and they had hopes of his ‘useful talents’. He had evidently already studied the assimilation of the laws of Ireland to those of Great Britain in Treasury business.
Trench was returned unopposed in 1802 and on 23 Nov. proposed the vote of thanks for the address, taking the pacification of Ireland and of Europe as his theme. In voting for the supply, 11 Mar. 1803, he justified rearmament as a defensive rather than an aggressive measure. He was now styled Viscount Dunlo, having with Castlereagh’s help obtained the peerage of Clancarty for his father. His colleague Richard Martin, who admitted that Dunlo was ‘a man of business and keeps his affairs in excellent order’ and that he was ‘punctual’ in his parliamentary attendance, resented what he regarded as government’s favouritism towards him, and in August 1803 carried a pro-Catholic resolution in defiance of a loyal (and protestant) address engineered by Dunlo for the Galway assizes. He continued to intervene in debate on Irish affairs, notably as a select committeeman on Irish finances in defence of the Irish bank restriction bill, 13 Feb. 1804. He twice tried in vain to come to the defence of the Irish government on 7 Mar. 1804.
When his friends returned to power in 1807, Clancarty was returned for Rye on the Treasury interest, but never took his seat because his appointment as joint postmaster-general in Ireland, which disqualified him, took place five days before the date of his return. He was in any case wanted in Ireland to reform the post office. Nothing came of Saunders Dundas’s notion of sending him to India in 1808 as head of a three-man commission of inquiry with a step in the peerage.
