Neville was returned for the vacant seat at Thirsk in 1805 by Sir Thomas Frankland, a political adherent of his uncles, Lords Grenville and Buckingham. Like the other Grenvillites, he voted against Melville, 8 Apr. and 12 June 1805, but was included, quite inexplicably, among the supporters of Pitt in the ministerial list of July. While he gave general support to his relatives in power in 1806 and voted for the repeal of the Additional Force Act, 30 Apr., he evidently cast at least one wayward vote, on the limited service clause of the mutiny bill, 30 May.
Neville drew no attention to himself in the 1807 Parliament, when he silently followed the Grenvillite Whig line, with votes against government on the Copenhagen expedition, 3 and 8 Feb. 1808; the convention of Cintra, 21 Feb. 1809; the Duke of York scandal, 15 and 17 Mar. 1809; the Walcheren fiasco in 1810; the Regency proposals, 1 and 21 Jan. 1811; the state of Ireland, 4 Feb., and the call for a stronger administration, 21 May 1812. Lengthy interludes between some of these votes suggest that he was an indifferent attender. He was absent from the House when Brand’s parliamentary reform proposals were debated, 21 May 1810,
Neville stood for Berkshire on Vansittart’s retirement in 1812 and came second in a contest forced by a radical reformer, who made him the special object of his attack as ‘the son of a great pensioner, and the nephew of three great pensioners’. If the reports of his speeches on the hustings are to be believed, Neville exaggerated when he claimed to have ‘always voted for the abolition of every sinecure and pension’, and to have supported ‘all the motions’ for parliamentary reform, though he may well have voted for Brand’s motion to extend the county vote to copyholders, 8 May 1812, when he and his opponent were already in the field for Berkshire. Nor does the division list support his claim that he had voted for Madocks’s charges of corruption against Perceval and Castlereagh, 11 May 1809. It seems clear that he pledged himself to support some measure of reform.
Whether as the result of electoral pressure, or of the influence of his cousins, Lords Nugent and Ebrington, or of personal inclination released from inhibition by his emancipation from Grenvillite control of his seat, Neville took a more progressive opposition line in the 1812 Parliament and was at odds with his senior relatives on several occasions. He went further even than Nugent by voting for the amendment condemning a war of proscription against Buonaparte, 25 May 1815. He took an active part in the post-war campaign for economy and retrenchment and spoke against the property tax, 18 Mar. 1816. To the vexation of his cousin, the 2nd Marquess of Buckingham, he opposed the first and third readings of the suspension of habeas corpus, 26 and 28 Feb. 1817.
At the general election of 1818, when he was challenged again by his radical opponent of 1812, Neville came top of the poll, having declared himself favourable to inquiry into a ‘mild, temperate and practicable’ instalment of reform, but hostile to ‘those disgusting theories, universal suffrage and annual parliaments’. His refusal to sign the requisition to Tierney, despite his ‘complete approval’ of the plan to install him as leader of the opposition, was evidently in character, for Lord Duncannon observed that his objection was only to putting his name to anything, and that he ‘never will attend party meetings’.
While Neville retained his opposition sympathies, his ardour may have cooled, for he appears on their side in only nine of the divisions of the 1819 session for which lists survive. He voted for Tierney’s motion on the resumption of cash payments, 2 Feb., and for the addition of Brougham to the committee of inquiry, 8 Feb.; against the Windsor establishment, 22 and 25 Feb.; for economies at the Admiralty, 18 Mar., and for inquiry into Scottish burgh reform, 6 May 1819. He did not vote either way on Tierney’s censure motion, 18 May (five days after his marriage), nor did he support Burdett’s detailed reform proposals, 1 July. His reaction to the Manchester massacre and its aftermath was the subject of anxious speculation among his Grenvillite relatives. His uncle Tom was pleased to hear that he had ‘pronounced, in the most decided manner, in private society, against the reformers’; he did not attend the Berkshire protest meeting, and on the eve of the emergency session Lord Buckingham believed that he would be ‘all right’. It was therefore ‘contrary to expectation’ that Neville voted against the address, 24 Nov. 1819.
Neville, whose literary works included an edition of Pepys’ Diary (1825) and a History of Audley End (1835), died 13 Mar. 1858.