He was the second son of Charles Spencer, 3rd Duke of Marlborough, and the Hon.

George Spencer, 4th Duke of Marlborough, was his elder brother.

[1] Spencer sat as Member of Parliament for Oxfordshire from 1761 to 1790 and 1796 to 1801[2] and was sworn of the Privy Council in 1763.

[3] He served as Comptroller of the Household from 1763 to 1765, as a Junior Lord of the Admiralty from 1768 to 1779 and as Treasurer of the Chamber from 1779 to 1782, when that sinecure post was abolished.

[5] Together, they had three sons:[6] Lady Spencer died in January 1812 aged 68.