Thomas Pelham was first returned to the Commons to fill a vacated seat for East Grinstead shortly after the convening of the last session of the Cavalier Parliament in October 1678. He was returned for the same borough in the subsequent election, and from that point until he voluntarily stood down before the election of 1705 he sat in every Parliament. During those long years in the Commons, he allied himself with first the Exclusionists and later the Whigs but always maintained an independent ‘country’ stance. He was influenced, in part, by his first father-in-law, the former attorney-general and firm advocate of Exclusion, Sir William Jones‡. His wife Elizabeth, Jones’s daughter, died within two years of the marriage, and in April 1686 Pelham made a marriage alliance with an even more prestigious and powerful Whig family when he married Grace, daughter of another Exclusionist, the melancholy Presbyterian peer, Gilbert Holles, 3rd earl of Clare.
From this point Pelham’s career was closely linked with his new brother-in-law, John Holles, who became 4th earl of Clare in 1689. By 1694, through his marriage to a daughter (and as of 1691 sole heiress) of Henry Cavendish, 2nd duke of Newcastle, and a fortuitous inheritance from a distant cousin, Clare had become one of the greatest landowners in England; he was himself created duke of Newcastle in 1694. It was perhaps through the influence of Newcastle that Pelham rose to prominence during the reign of William III. His resignation from the treasury commission in late February 1692 was a gesture of support for his brother-in-law’s resignation of his court offices over William’s refusal to grant his demand for the dukedom of Newcastle. In the Commons Pelham maintained his Whig stance but did not follow the Junto consistently, often taking an independent line, as in his opposition to the attainder of Sir John Fenwick‡. His connection with the Whigs, was further strengthened by the marriage in 1698 between his daughter, Elizabeth (with a portion of £30,000) and a prominent Whig politician, Charles Townshend, 2nd Viscount Townshend.
Pelham returned to the treasury commission in May 1697 but was removed from it again in June 1699. Reappointed in March 1701 he lost office again at Anne’s accession.
Perhaps Pelham withdrew from the Commons to further emphasize his desire for a peerage; the growing influence of his patron, Newcastle, in the government ensured that his wish for further favour would eventually be gratified. Under constant pressure from Harley and the ‘duumvirs’, throughout 1705-6 Anne provided offices and honours to an increasing number of Whigs, often against her own judgment. In December 1706 Harley and Sidney Godolphin, earl of Godolphin, included Pelham among their list of ten Whigs who were to be either created peers or elevated from their existing titles.
If Pelham was created a baron in order to increase Whig numbers and voting power, his subsequent record in the House would have been a disappointment to his brother-in-law and those who promoted him. His activity and attendance remained low over the next six years. After coming to 22 sittings of the House from the time of his introduction, he left the House for that session on 14 Mar. 1707, just when proceedings on the bill of Union were heating up, and did not come at all in the brief session of April 1707. He was present at 15 of the sittings in 1707-8, first sitting in this session on 10 Nov. 1707. Even when the Whigs dominated Parliament, as they did after the 1708 elections, Pelham seldom showed up in the House, and he came to only 16 meetings of the 1708-9 session. At this point his attitude to the two principal ministers, the ‘duumvirs’ Godolphin and John Churchill, duke of Marlborough, was ambivalent. For while he obsequiously solicited Marlborough in March 1709 for a military commission for his kinsman, James Pelham‡, in the House he joined with Newcastle and the Junto Whigs against the increasingly beleaguered Godolphin.
Even though Newcastle was the only Whig to remain in office throughout the change of ministry in the summer and autumn of 1710, Pelham barely bothered to come to the Tory-dominated Parliament. He came to only nine sittings in the 1710-11 session. He was perhaps summoned or encouraged to appear in the House for these few brief meetings in early 1711, for he put his name to the two protests of 3 Feb. 1711 objecting to the House’s condemnation of the previous ministry for its failure to supply the forces in Spain adequately to counter the Franco-Spanish army at Almanza. Two days after this protest he left the House and registered his proxy with Newcastle, who himself did not return to the House from a period of absence until 19 February.
For the following (1711-12) session Thomas Howard, 6th Baron Howard of Effingham, registered his proxy with Pelham on 1 Dec. 1711. Pelham sat for 12 sittings from the session’s first day on 7 Dec. until 25 Jan. 1712 when he once again left the House, probably due to illness. He registered his proxy with Godolphin on 31 January.
Pelham died, apparently of apoplexy, on 23 Feb. 1712 at his house of Halland at Laughton and reportedly ‘left his son ... the richest heir in England’.
