As an Oxford undergraduate, Mordaunt toured the north of England and Scotland with his friend William Ralph Cartwright. He served with the militia at the scene of the naval mutiny in 1797 and against the Irish rebels a year later. He ruined his health in Ireland and went to Portugal to recuperate in 1803, but suffered from asthma for the rest of his life.
He was at once listed a supporter of Pitt, but raised doubts about this after voting in the majorities against Melville, 8 Apr., 12 June 1805. On 3 Mar. 1806 he was in the minority against Ellenborough’s seat in Lord Grenville’s cabinet. Eight days later he presented the Warwickshire maltsters’ petition for relief from malt duties and on 9 May opposed the iron duty bill to please his Birmingham constituents. He was an infrequent speaker from ‘sensitive shyness’. Like his father he was friendly to the abolition of the slave trade. On 17 Feb. 1807 he was given leave to bring in a bill for the recovery of small debts in Birmingham, but defaulted early in March. On 21 Mar. 1808 he took a month’s leave after serving on the Malton election committee. His only known vote against the Portland ministry was on the allegation of ministerial corruption, 25 Apr. 1809. On 11 May he had his moment of glory when, with Cartwright, he led the opposition to Madocks’s bid to turn the question into a reform issue, but it has been snatched from him by the misattribution of his speech.
Mordaunt’s conduct over the orders in council, which were so much resented by his Birmingham constituents, did not give them satisfaction. On 17 Apr. 1812, presenting their petition against them, he allowed himself some levity, though he said he would support a committee of investigation and conceded (28 Apr.) that the manufacturers’ distress was a burden on the poor rates. His only other known gesture in the House that session was to support inquiry into conditions at Lincoln gaol, 25 June. At the dissolution attempts were made by his Birmingham critics to conjure up an opposition to him at the general election, but they failed.
He was listed a Treasury supporter after the election and suggested as a seconder of the Speaker’s re-election in October 1812.
Mordaunt was spared a contest in 1818, having doubtless satisfied many of his critics of his independence. He opposed alteration in the coal duties, 2 Feb. 1819, and was one of the midland Members who lobbied the prime minister on the issue on 8 Feb.
