The turning point in his political fortunes was the marriage of his sister Hester in 1754 to William Pitt, later Earl of Chatham. Although Lord Temple had no outstanding qualities, his political career became linked with that of his brother-in-law. In November 1756 Temple became First Lord of the Admiralty in the ministry of Devonshire and Pitt. He was intensely disliked by George II, who dismissed both him and Pitt from office in April 1757. But when the memorable coalition cabinet of Newcastle and Pitt was formed in June of the same year, Temple received the office of privy seal. He was the only member of the cabinet who supported Pitt's proposal to declare war with Spain in 1761, and they resigned together on 5 October.
Later career
From this time Temple became one of the most violent and factious of politicians, and it is difficult to account for the influence he exerted over his illustrious brother-in-law. He himself is said to have avowed that "he loved faction, and had a great deal of money to spare." He was on bad terms with his younger brother, George Grenville, when the latter became first lord of the treasury in April 1763, and he had no place in that ministry; but the brothers were reconciled before 1765, when Temple refused to join the government and persuaded Pitt to refuse likewise. A few weeks later the king offered the most liberal terms to induce Pitt to form or join an administration; and "a ministry directed by that great statesman," says Lecky, " would have been beyond all comparison the most advantageous to the country; it had no serious difficulty to encounter, and Pitt himself was now ready to undertake the task, but the evil genius of Lord Temple again prevailed. Without his co-operation Pitt could not, or would not proceed, and Temple absolutely refused to take office even in the foremost place." Pitt's continued refusal to join the first Rockingham administration was no doubt partly due to the same disastrous influence, though before the close of 1765 the old friendship between the brothers-in-law was dissolving; and when at last in July 1766 Pitt agreed to form a government, Temple refused to join; being bitterly offended because, although offered the Treasury, he was not to be allowed an equal share with Pitt in nominating to other offices. Temple then began to libel Pitt; and in conjunction with his brother George he concentrated the whole Grenville connection in hostility to the government. After George Grenville's death in 1770 Lord Temple retired almost completely from public life. Lord Temple was a great intriguer, and is said to have been the author of several anonymous libels, and the inspirer of many more. Macaulay's well-known comparison of him with a mole working below "in some foul, crooked labyrinth whenever a heap of dirt was flung up," which perpetuates the spleen of Horace Walpole, perhaps exceeds the justice of the case; but his character was rated very low by his contemporaries. In private life he used his great wealth with generosity to his relations, friends and dependents. Pitt was under pecuniary obligation to him. He was the principle backer behind The North Briton weekly newspaper, and he paid the costs incurred by John Wilkes in litigation. He also provided Wilkes with the freehold qualification which enabled him to stand for Middlesex in the famous election of 1768. Although known as a man given to confrontation and strife, Earl Temple did get involved with one of London's most fashionable charities of his time. He served as a vice president for the Foundling Hospital from 1760 to 1768, which was dedicated to the salvation of the large number of children abandoned by their parents in London each day. It cannot be ruled out that his involvement in this charity was motivated purely by compassion. However, it is possible that it also had to do with the achievement of status and access to other notable supporters, such as the Duke of Bedford, Lord Vere Beauclerk, and the Earl of Dartmouth, among others. In addition to the estates he inherited, Temple gained a considerable fortune by his marriage in 1737 with Anne, daughter and co-heiress of Thomas Chambers of Hanworth, Middlesex; a volume of poems by her was printed at the Strawberry Hill Press in 1764.
