Charles Spencer, third Earl of Sunderland, who was born in 1674, was the second son of Robert, second Earl, by Anne, daughter of George Digby, second Earl of Bristol. He appears, even when a boy, to have displayed much ability, for as early as 1688, Evelyn, who was on very intimate terms with the Spencer family, mentions him as 'a youth of extraordinary hopes, very learned for his age, and ingenious, and under a governor of great merit.' This governor appears to have been Dr. Trimnell, afterwards Bishop of Winchester. When quite young, Lord Spencer manifested a great love for books, and already possessed a considerable collection of them, for he was but twenty years of age when Evelyn wrote to him: 'I was with great appetite coming to take a repast in the noble library which I hear you have lately purchased.' Evelyn's Diary also contains several notices of the collection, and particularly mentions the purchase of the books of Sir Charles Scarborough, an eminent physician, which were at one time destined for the Royal Library.

At the general election in 1695 Lord Spencer was returned both for Tiverton in Devonshire, and for Heydon in Yorkshire. He elected to sit for Tiverton, which he represented in Parliament until the death of his father in 1702, when he succeeded to the title, his elder brother having died in 1688. While a member of the House of Commons he appears to have held opinions of a somewhat republican nature; and Swift tells us, 'he would often, among his familiar friends, refuse the title of Lord (as he had done to myself), swear he would never be called otherwise than Charles Spencer, and hoped to see the day when there should not be a peer in England.' These views, however, were very considerably modified on his succession to the title. In 1705 he was appointed envoy extraordinary and plenipotentiary to the Court of Vienna, to congratulate the Emperor Joseph on his accession to the crown. Shortly after his return to England, Sunderland, notwithstanding the opposition of Queen Anne, who always entertained a great antipathy for him, was made one of the Secretaries of State, an office which he held until June 1710, when he was dismissed by the Queen, who wished, however, to bestow on him a pension of three thousand pounds a year. This he refused, with the remark, 'I am glad your Majesty is satisfied I have done my duty. But if I cannot have the honour to serve my country, I will not plunder it.' He remained out of office during the remainder of Anne's reign, but on the accession of George I. to the throne he was made Lord-Lieutenant of Ireland. This post, however, was by no means agreeable to him, for he regarded it as a kind of banishment, and during the short time he held it he never crossed the Channel. In 1715 he was appointed Lord Privy Seal, Vice-Treasurer of Ireland in 1716, and in April 1717 he was a second time made a Secretary of State, his friend Addison receiving a like appointment. On the 16th of March 1718 he became Lord-President of the Council, and on the 21st of the same month First Lord Commissioner of the Treasury, which office he resigned on the 3rd of April 1721. He died, after a short illness, on the 19th of April 1722.

Lord Sunderland was thrice married, and had children by all his wives. By his second wife, Anne, daughter of the great Duke of Marlborough, he had four sons and a daughter. The eldest son died in infancy; Robert, the second, succeeded to the earldom, and died unmarried on the 15th of September 1729; Charles, the third, became Earl of Sunderland on the death of his elder brother, and in 1733 second Duke of Marlborough, but he did not obtain the Marlborough estates until the demise of the Dowager Duchess in 1744; John, the youngest son, who, by a family arrangement, then succeeded to the Spencer estates, was the father of the first Earl Spencer.

Lord Sunderland was a most liberal patron of literature, and the splendid library which he commenced in his early youth, and sedulously augmented till the time of his death, bore witness for several generations to his love of books. This noble collection was kept in his town house, which stood between Sackville Street and Burlington House, where it occupied five large rooms, and at the time of the Earl's death in 1722 consisted of about twenty thousand printed volumes, together with some choice manuscripts, and was valued at upwards of thirty thousand pounds; the King of Denmark being anxious to purchase it of his heirs for that sum. Charles, the fifth Earl, also took great interest in the library, and added a considerable number of books to it, among which was a copy on vellum of the Livy of 1470, printed at Venice by Vendelin de Spira. Only one other perfect copy on vellum of this edition is known to exist. In 1749 the library was removed to Blenheim, where it remained until 1881. It was sold by Puttick and Simpson in five portions in 1881, 1882 and 1883, and the entire sale, which consisted of thirteen thousand eight hundred and fifty-eight lots, realised fifty-six thousand five hundred and eighty-one pounds, six shillings.

Lord Sunderland was always very liberal in his dealings with booksellers, and the prices which he gave for his books frequently gave umbrage to other collectors. Humphrey Wanley, Lord Oxford's librarian, when giving in his Diary an account of a book-sale which took place in 1721, mentions that: 'Some books went for unaccountably high prices, which were bought by Mr. Vaillant, the bookseller, who had an unlimited commission from the Earl of Sunderland. The booksellers upon this sale intend to raise the prices of philological books of the first editions, and indeed of all old editions, accordingly. Thus Mr. Noel told me that he has actually agreed to sell the Earl of Sunderland six ... printed books, now coming up the river, for fifty pounds per book, although my Lord gives no such prices.' And on the demise of the Earl, Wanley wrote: 'This day died the Earl of Sunderland, which I the rather note here, because I believe by reason of his decease some benefit may accrue to this Library, even in case his relatives will part with none of his books. I mean, by his raising the price of books no higher now; so that, in probability, this commodity may fall in the market, and any gentleman be permitted to buy an uncommon old book for less than forty or fifty pounds.'