Vanneck and his elder brother were partners in the London mercantile house in Broad Street they inherited from their father, who was of Dutch extraction. In 1790 his brother made way for him as Member for Dunwich on the family interest in an unsuccessful bid for the county and died unmarried a year later. Joshua thereby inherited, with the baronetcy, estates estimated at £8,000 a year and the bulk of ‘between £200,000 and £300,000’.
Like his brother, Vanneck was a Portland Whig with nothing to say in debate; unlike him he was not a regular attender. He voted against Pitt’s Russian policy, 12 Apr. 1791 and 1 Mar. 1792, and was listed favourable to repeal of the Test Act in Scotland in 1791. He appeared in no further minorities in that Parliament, being listed a Portland Whig in December 1792 and suggested as a possible recruit for the ‘third party’ early in 1793. It was to Portland that he wrote, 20 July 1794, soliciting a peerage. The duke replied that he would seek the ‘first favourable opportunity’ of procuring him one, though he could make no promises:
The support I uniformly received from your late most worthy brother, during the whole of his political life, and the sanction which you have given to my opinions by your parliamentary conduct, are circumstances on which I reflect with no less pride than gratitude.
That Vanneck’s conversion was not much noticed is suggested by his appearing as ‘con’ in a Treasury list of 1795. His only known vote in the next session was in the majority against the abolition of the slave trade, 15 Mar. 1796, and Pitt, writing to the Irish viceroy to recommend him (by the wrong Christian name) as one of two Irish peers to be created at the dissolution, 9 June, remarked: ‘The other is Sir Gerard Vanneck, for whom the Duke of Portland is anxious, and who has the merit of being a very rich man, and I believe a very zealous convert’. Portland soon afterwards obtained the King’s assent to the creation.
Huntingfield (his new title) subscribed £40,000 to the loyalty loan for 1797 and voted for the bonus to subscribers, 1 June 1797. He supported Pitt’s assessed taxes, 4 Jan. 1798. His sister Gertrude was until her death that year a lady of the bedchamber to the Princess of Wales and ‘a great sycophant to the Prince’.
Huntingfield might be expected to support Portland’s ministry 1807-9, but he was reported to be absenting himself in Perceval’s first session in office. In fact, he voted for the address, 23 Jan. 1810, and subsequently abstained. The Whigs listed him ‘Government’ in March 1810. At that time there was a rift between him and the Barne family over the latter’s management of the borough of Dunwich, but it was composed.