A love match, the marriage resulted in the births of three surviving children, who included Georgiana Cavendish, Duchess of Devonshire.

The Spencers became earl and countess in 1765, a reward granted by the Duke of Newcastle for John's political loyalty to the Whig party.

[3] In 1754, seventeen-year-old Georgiana Poyntz met twenty-year-old John Spencer,[4][5] who had inherited enormous wealth from his great-grandmother, Sarah Churchill, Duchess of Marlborough.

On his return they recognised their love had persisted, and shortly after his birthday they married in a secret ceremony on 20 December 1755 at Althorp, the Spencer family seat in Northamptonshire.

[10] A Whig, in 1756 John entered the House of Commons as MP for Warwick, and in 1761 was awarded a viscountcy by the leader of the party, the Duke of Newcastle.

[11] According to biographer Donna T. Andrew, Lady Spencer was "exceptionally intelligent and well educated"; she was fluent in French and Italian, possessed some knowledge of Greek, and was "accomplished in botany.

An extravagant man, he left their son with enormous debts, but, according to Richard Milward, also "greatly increased his family estates and its prestige by being the employer of leading architects, the collector of Italian paintings.

Lady Spencer stayed with them for ten days to help care for the child, finding that Caroline only slept when sleeping with her grandmother.