Thomas Pitt now became owner of the controlling interest in the rotten borough of Old Sarum and a considerable share in that of Okehampton in Devon.

[2] Pitt was one of the seventy-two whig members who met at the Thatched House Tavern, London, on 9 May 1769, to celebrate the rights of electors in the struggle for the representation of Middlesex; he seconded Sir William Meredith in his attempt to relax the subscription to the Thirty-nine Articles, and he spoke against the Royal Marriage Bill.

Horace Walpole, who quarrelled with him on political topics, calls him a 'flimsy' speaker, but Wraxall remarked that, although he rarely spoke, his family position guaranteed him an audience when he did.

In February 1783, he moved the address for the Shelburne ministry, protesting that he had always been opposed to the use of force against the American colonies, and he attacked Charles James Fox's East India Bill.

Next year, when the same question was brought forward, he was ridiculed for a change of opinion, and his offer to sacrifice his rotten borough for the public good.

On 5 January 1784 he was raised to the peerage as Baron Camelford of Boconnoc, a promotion attributed to the influence of his cousin William Pitt the Younger.

He was then the neighbour of Horace Walpole of Strawberry Hill House, who recognised his skill in Gothic architecture, and went so far as to call him 'my present architect.'

Thomas Pitt also built Camelford House, fronting Oxford Street, at the top of Park Lane, London; and as a member of the Dilettanti Society, to which he had been elected on 1 May 1763, he proposed in February 1785 that the shells of two adjoining houses constructed by him in Hereford Street should be completed by the society for a public museum, but financial considerations put a stop to the project.

Pitt was a friend of Mary Delany, to whom he gave for her lifetime portraits of Sir Bevil Grenville, his wife, and his father, and he proposed to John Maurice, Count of Brühl that they should jointly assist Thomas Mudge in his plans for the improvement of nautical chronometers.

A few days after his elevation to the peerage a pamphlet, in which 'the constitutional right of the House of Commons to advise the sovereign' was upheld, was attributed to Camelford, and referred to in parliament by Burke, who also ridiculed him as the alleged author of a tract relating to parliamentary reform.

She died at Camelford House, Oxford Street, London, on 5 May 1803, aged 65, pining from grief at the career of her son, and was buried in the vault in Boconnoc churchyard on 19 May.

Thomas and Anne had two children: Hester Thrale described Pitt as 'a finical, lady-like man'[3] and Sir J. Eardley-Wilmot dubbed him in 1765 'the prince of all the male beauties,’ and 'very well bred, polite, and sensible'.