MP for Stafford
Monckton first contested the Stafford Borough constituency in the general election of 12 September 1780. Stafford was generally described as “venal” and it was very expensive to contest. This was because it was no longer a pocket borough, as it had been until a few years earlier, when it was controlled by the Chetwynds of Ingestre Hall. Around 1774, the Chetwynds had lost control, although family members would represent the borough again in the future, and the electorate, mostly tradesmen, were free to sell their vote to the highest bidder. It took 258 votes for Monckton to top the poll. Richard Brinsley Sheridan, standing jointly with Monckton as a Whig, got 248 votes and was declared Stafford's second MP, after apparently paying 5 guineas to each elector. Sheridan, a close friend of Mary Monckton, was to have a brilliant parliamentary, as well as literary, career but Monckton himself made a much slighter impression. Although he was to remain MP for Stafford for 32 years, 26 of them in harness with Sheridan, there is no record that he ever spoke in a debate, although he did attend frequently, took part in numerous divisions and was active for some years in Whig factional politics.
The overarching issue in the early years was the American Revolutionary War, which Britain was in the process of losing, and in which Monckton's brother Henry had been killed at the Battle of Monmouth in 1778. The war was rapidly eroding support for Lord North's ministry, and Monckton voted consistently against North's government in its dying days, siding with the Rockingham Whigs. However, Rockingham himself died shortly after replacing North in 1782. The new leader, Shelburne, failed to maintain Whig unity. Disputes focussed superficially on the ambiguity of Shelburne's peace manoeuvres, although there was actually a strong personal rivalry between Shelburne and the radical Charles James Fox. Both Monckton and Sheridan sided with the Foxite faction and voted against the Shelburne ministry on the peace negotiations, bringing it down in favour of a short-lived and unpopular Fox-North Coalition.
One of the coalition ministry's most important measures was an East India Bill, designed to nationalise the East India Company. Monckton, obviously an expert on the subject, voted for the bill on 27 November 1783. George III personally ensured that the bill was thrown out by the House of Lords, then dismissed the government and appointed William Pitt the Younger prime minister. Monckton and Sheridan were returned unopposed in the ensuing general election, probably because their wealth made a contest pointless. However, large numbers of Whigs lost their seats, becoming known as "Fox's Martyrs", and Pitt was able to form a secure Tory administration.
Over the next few years, Monckton consistently voted against Pitt's ministry. He joined the Whig Club on 4 April 1785. The Whig party was increasingly divided between the rump of the Foxite faction and a mainstream grouping around William Cavendish-Bentinck, 3rd Duke of Portland The Portland Whigs made overtures to Monckton and he met with them on 11 May 1790. He and Sheridan again topped the poll at Stafford in the general election of June 1790, with exactly 264 votes each. Monckton's acceptance into the Whig elite was formalised by membership of Brooks's Club, for which he was sponsored by Portland himself on 7 February 1791.
The outbreak of the French Revolution in 1789 was already causing internal schism and regrouping among the Whigs, but for some time Monckton continued to vote for radical and liberal measures and against the government. In April 1791 he supported repeal of the Test Act in Scotland, a measure intended to begin the process of restoring civil rights to Roman Catholics and Nonconformists. On 1 March 1792 he voted with the Whigs against the government's intervention on the Ottoman side in the Russo-Turkish War. However, with most of the Portland Whigs, he supported the government's entry into the French Revolutionary Wars, while the Foxites continued to oppose war. In 1794, Portland accepted the post of Home Secretary from Pitt. Thereafter, the Portland Whigs disappeared as a distinct faction Portland was considered a Tory, although he was to prove a rallying point within the party for dissident, liberal Tories like George Canning.
Monckton too tended to support the government throughout the French Revolutionary and Napoleonic Wars. However, he took an independent line on many issues. In 1803 he supported John Calcraft's defence of the Prince of Wales's financial position: the Prince was closely associated with the Whig opposition. He also gave general support to Ministry of All the Talents, headed by the Whig Grenville during 1806–7. However, he contacted Speaker Abbot, a Tory who was popular with all parties, to assure him of support should the ministry try to dislodge him. He sided with the Whigs throughout the Regency crises of 1810 and 1811, but voted against Parliamentary reform in 1810.
Monckton was returned unopposed, with Sheridan, in 1796 and 1802. In 1806 and 1807 he was elected alongside Richard Mansel Philipps, a radical Whig who was soon mired in scandal over debt and fraud. In 1812 Monckton announced his retirement from Parliament and did not stand for election again.