Henrietta Ponsonby, Countess of Bessborough (16 June 1761 – 11 November 1821), born Lady Henrietta Frances Spencer (generally called Harriet), was the wife of Frederick Ponsonby, 3rd Earl of Bessborough; the couple were the parents of Lady Caroline Lamb.

Being the youngest child, Harriet was often left in England when her parents and elder sister Georgiana would visit the continent for her father's health.

[3] Tired of Duncannon's abuse and craving love in her life, Harriet began a disastrous affair with Richard Brinsley Sheridan.

Their fears were often proven, as when he threatened violence if Harriet did not hand over her marriage settlement to him after losing an especially ruinous gambling round.

[6] Perhaps chastened by time and age, by 1820 Duncannon rather miraculously ceased his abuse, and he and Harriet eventually settled into a companionable marriage.

Harriet managed to hide her pregnancies from her husband; this was less difficult in an era when the aristocracy might make extended visits of many months abroad or to friends' country homes.

[8] Recognizing his need to marry for purposes of his political career, she did not oppose, and in fact, facilitated Granville's marriage to her niece, Lady Harriet Cavendish ('Harryo') in 1809.

[9][10] Of her younger admirers, Harriet's favourite was The Honourable William Lamb (who succeeded as the 2nd Viscount Melbourne in 1828), although he then fell in love with her daughter Caroline.

Although Harriet was anxious for Caroline to marry early, she had misgivings (which would come to be entirely justified) as to whether William and Caroline were well suited; in addition, she and William's mother Elizabeth Lamb, Viscountess Melbourne, detested each other (Harriet referred to the shrewd and coldly pragmatic Lady Melbourne as "the Thorn").

Harriet died on 11 November 1821, in Florence, Italy, at the age of 60, following the death of her youngest grandchild, Henry, in Parma.