William Cavendish, 5th Duke of Devonshire (1748-1811) was the eldest of the four children of William Cavendish, 4th Duke of Devonshire and his wife, Charlotte Elizabeth Boyle, Baroness Clifford (1731-1754), daughter and heir of Richard Boyle, third earl of Burlington. He was known by the courtesy title Lord Cavendish until his mother's death, when he succeeded her as seventh Baron Clifford; from his father's accession to the Dukedom in 1755 he was known as Marquess of Hartington. On his father's death on 3 October 1764 he became 5th Duke of Devonshire and inherited vast estates in England and Ireland valued at over £36,000 a year. These included the properties of Chatsworth House and Hardwick Hall in Derbyshire, Londesborough House and Bolton Abbey in Yorkshire, Lismore Castle in co. Waterford, Chiswick House in Middlesex, and Devonshire House and Burlington House in Piccadilly, London. Further family estates were settled on his brother George, later first earl of Burlington. After the deaths of his parents Devonshire was brought up by his three bachelor uncles – Lords Frederick, George, and John Cavendish – and was presented at court in the spring of 1765. He travelled on the continent in 1767-1768, and his uncles kept him informed of their management of his interest at the 1768 general election.
On 7 June 1774 Devonshire married the seventeen-year-old Lady Georgiana Spencer (1757-1806). Georgiana bore him three children: Georgiana Cavendish (1783–1858), Harriet Cavendish (1785–1862) and William George Spencer Cavendish (1790-1858, later 6th Duke of Devonshire). Before his marriage he had fathered an illegitimate daughter, Charlotte Williams, by a London milliner, Charlotte Spencer (d. 1781).
Devonshire came from one of the wealthiest and most powerful Whig families. However, he possessed no great political ambition. He was Lord High Treasurer of Ireland and governor of Cork from 1766 to 1793, and Lord Lieutenant of Derbyshire from 1782 to his death, but three times refused cabinet office. He was appointed a Knight of the Garter on 19 April 1782.
In May 1782 the Devonshires met Lady Elizabeth Foster (1757-1824), daughter of Frederick Hervey, 4th earl of Bristol, bishop of Derry, and estranged wife of John Thomas Foster MP. Together the three formed a ménage à trois whose conspicuous interdependence provoked much gossip and speculation. Lady Elizabeth gave birth to two children fathered by the Duke: Caroline St Jules (1785-1852), and Augustus William James Clifford (1788-1877), later a naval officer and a baronet.
Devonshire House remained the focus for the Foxite Whigs through the 1790s. The Duke regarded himself as bound to the Whig tradition by heredity. He was not a natural leader, and those who thought he could succeed Fox as the focus of the whig party when Fox temporarily retired from politics were disappointed.
From middle life the Duke increasingly suffered from bouts of ill health and spent less and less time in London, preferring Chatsworth, Chiswick, or visits to Bath. The death of Georgiana in 1806 shook his life both personally and politically. Lady Elizabeth Foster took over as female head of the household and they married at Chiswick House on 19 October 1809.
Devonshire died at Devonshire House, Piccadilly, London, on 29 July 1811 and was buried at All Saints' Church, Derby. He left an estate estimated at £125,000, but expenditure on the acquisition of land and on property development during his lifetime, including The Crescent at Buxton, Derbyshire, as well as the burden of Georgiana's gambling losses and the other demands of the Devonshires' expensive lifestyle, had burdened the estate with debts calculated at £593,000 in 1814.
Principal source: Michael Durban, 'Cavendish, William, fifth duke of Devonshire (1748-1811)', Oxford Dictionary of National Biography (Oxford: Oxford University Press, 2004).