George Spencer was the eldest son of George Spencer, 4th Duke of Marlborough, and Lady Caroline Russell. He was educated at Eton and Christ Church, Oxford, where he graduated M.A. in 1786, and D.C.L. in 1792. He was Member of Parliament for Oxfordshire from 1790 to 1796 and for Tregony from 1802 to 1804. From 1804 to 1806 he was one of the Lords of the Treasury, and in the latter year was called to the upper house as Baron Spencer of Wormleighton. He married, in 1791, Susan, second daughter of John Stewart, seventh Earl of Galloway. In 1817 he succeeded to the Dukedom and took the additional name of Churchill. He spent great sums on the gardens and library at White Knights. Because of his extravagance, he was compelled to disperse most of his collections during his own lifetime. The White Knights Library was sold by R. H. Evans in two parts, on 7 and 22 June 1819, and the complete set of the Aldine Classics on 24 May 1820.