She was born after nine years of childless marriage between William Cavendish, 5th Duke of Devonshire, and his wife, Lady Georgiana Spencer, the political hostess and socialite.

[4] Called "Little G" by her mother, the baby was named after Lady Georgiana and her aunt the Duchess of Portland, who also served as a godparent alongside Lord John Cavendish and the Prince of Wales, later George IV.

[5] The Duchess of Devonshire chose to breastfeed the infant herself and did not employ a wet nurse, an unusual decision for a member of the upper class; her husband's family was displeased with her choice, as they felt it conflicted with the task of birthing a male heir.

[6] A month after her birth, "Little G" was christened alongside her cousin Frederick at the church in Wimbledon Park – the same place the Duke and Duchess married nine years earlier.

[2] In the early 1790s, the Duke and Duchess separated after she bore an illegitimate child (Eliza Courtney) to her lover, Charles, Earl Grey.

[12] The two shared a love of books and other interests; the Duchess's biographer, Amanda Foreman, writes "Georgiana treasured Little G's company so greatly that she could never bear to say a harsh word towards her".

[15] Lady Holland observed Georgiana and described her as "a most charming girl–sensible, pleasing, full of information and totally without a particle of affectation, and if she bestows herself upon a man equal to her situation, I have no doubt she will make a most delightful wife".

No engagement occurred, however; to convince his daughter to agree to the match, the Duke of Devonshire offered Georgiana a £30,000 dowry and the use of their London residence Londesborough House.

She was surprised to discover that the family showed little affection to the children, in contrast to her own background being raised by her loving mother.

Harriet's son Frederick later wrote that the experience "strengthened the tie of sisterly affection, which bound them together during the whole of their joint lives".

[29] Historian Judith Lewis cites this opinion as evidence of the prevalence of class consciousness during the 19th-century, as Lady Carlisle was "one of the more inoffensive of the grand dames of her time".

[19] The 6th Duke of Devonshire died in 1858; in his will, he left his sister Georgiana Chiswick House in Middlesex, a favourite residence of their parents.