Lady Harriet Elizabeth was born on 29 August 1785. She was the daughter of Lady Georgiana Cavendish, Duchess of Devonshire (7 June 1757 - 30 March 1806) and William Cavendish, 5th Duke of Devonshire (14 December 1748 - 29 July 1811). Her maternal grandparents were Margaret Georgiana Poyntz (27 April 1737 - 18 March 1814) and John Spencer, 1st Earl Spencer (19 December 1734 - 31 Oct ober 1783). Her paternal grandparents were Charlotte Elizabeth Boyle, Baroness Clifford and Sir William Cavendish, 4th Duke of Devonshire. Lady Harriet's parents were married on on 5 June 1774. Her siblings included: Lady Georgiana Dorothy Cavendish (12 July 1783 - 8 August 1858) and William George Spencer Cavendish, 6th Duke of Devonshire (21 May 1790 - 18 January 1858). Nicnamed Harryo, she was also known as Henrietta. Her sister, Georgiana was nicknamed Little G and her brother, William George, nicknamed Hart. In May 1782, her parents met Lady Elizabeth Foster (13 May 1759 - 30 March 1824) in Bath. In 1776, she had married John Thomas Foster of Dunleer (1747-1796). The Fosters had three children: Frederick (1777-1853), Augustus (1780-1848) and Elizabeth (1778-1778). The couple separated and Foster retained custody of their sons. Lady Elizabeth became Lady Georgiana's closest friend and soon the mistress of the Duke. Lady Elizabeth bore two children by the Duke: a son, Augustus (1788-1877) and a daughter, Caroline St. Jules. Her mother, Lady Georgiana had a illegitimate daughter with Charles, 2nd Earl Grey, Eliza Courtney (20 February 1792 - 2 May 1859) born on 20 February 1792, in Aix en Provence, France. She grew up with her father's parents in Falloden, Northumberland. Her sister, Lady Georgiana Dorothy married George Howard, 6th Earl of Carlisle on 21 March 1801, at Devonshire House, in Piccadilly, London. Her cousin, Lady Caroline (1785-1828) married William Lamb in June 1805. Her mother, Lady Georgiana died on 30 March 1806. Her father, William married his second wife, Lady Elizabeth in 1809. Lady Harriet Elizabeth married Granville Leveson-Gower, 1st Earl Granville (12 October 1773 - 8 January 1846) on 24 December 1809. He was the son of Lady Susanna Stewart and Sir Granville Leveson-Gower, 1st Marquess of Stafford. He was the former lover of her aunt, Lady Henrietta. Granville had two illegitimate children with Lady Henrietta, George Stewart and Harriet Emma Arundel Stewart. Lady Harriet Elizabeth and Granville had four children.
The children of Lady Harriet Elizabeth Cavendish and Sir Granville Leveson-Gower, 1st Earl Granville:
Lady Susan Georgiana Leveson-Gower (- 30 April 1866)
Lady Georgiana Charlotte Leveson-Gower (-19 January 1885)
Granville George Leveson-Gower, 2nd Earl Granville ( 11 May 1815 - 31 March 1891)
Edward Frederick Leveson-Gower ( 3 May 1819 - 30 May 1907)
Her father, William died on 29 July 1811. He was succeeded by her brother, William George, known as "The Bachelor Duke." Lady Harriet Elizabeth Cavendish became Viscountess Granville of Stone Park on 12 August 1814. She became Countess Granville on 10 May 1833. Her husband, Lord Granville died on 8 January 1846. The 6th Duke of Devonshire died on 18 January 1858. Her sister, Lady Georgiana Dorothy died on 8 August 1858, at Castle Howard, Yorkshire, England. Lady Harriet Elizabeth died aged 77, on 25 November 1862.