| The Duke of Devonshire | |
| Honorific Prefix: | His Grace |
| Order1: | Lord Lieutenant of Ireland |
| Term Start1: | 1737 |
| Term End1: | 1744 |
| Monarch1: | George II |
| Predecessor1: | The Duke of Dorset |
| Successor1: | The Earl of Chesterfield |
| Order2: | Lord Steward |
| Term Start2: | 1733 |
| Term End2: | 1737 |
| Monarch2: | George II |
| Term Start3: | 1744 |
| Term End3: | 1749 |
| Monarch3: | George II |
| Order4: | Lord Privy Seal |
| Term Start4: | 1731 |
| Term End4: | 1733 |
| Monarch4: | George II |
| Successor4: | The Viscount Lonsdale |
| Birth Date: | 26 September 1698 |
| Death Date: | 5 December 1755 |
| Nationality: | British |
| Spouse: | Catherine Hoskins |
| Children: | 7 (including William Cavendish, 4th Duke of Devonshire, Lord John Cavendish, and Lord Frederick Cavendish) |
| Parents: | William Cavendish, 2nd Duke of Devonshire Rachel Russell |
William Cavendish, 3rd Duke of Devonshire, (26 September 1698 – 5 December 1755) was a British nobleman and Whig politician who sat in the House of Commons from 1721 to 1729 when he inherited the Dukedom.
Cavendish was the son of William Cavendish, 2nd Duke of Devonshire, and his wife, the Hon. Rachel Russell, and was known as Marquess of Hartington.
Like his father, Lord Hartington was active in public life. He was returned unopposed as member of parliament for Lostwithiel at a by-election in 1721. At the 1722 general election he was returned unopposed as MP for Grampound. He was also unopposed when he was returned as MP for Huntingdonshire at the 1727 general election. He surrendered the seat in 1729 when his father's death sent him to the House of Lords.[1] He was made a Privy Counsellor in 1731. He served as Lord Privy Seal from 1731 to 1733, when he was invested as a Knight of the Garter. He later served for seven years as Lord Lieutenant of Ireland.[2]
He sold the Old Devonshire House at 48 Boswell Street, Theobald's Road, in Bloomsbury, and in 1734 engaged the architect William Kent to build a new Cavendish House in fashionable Piccadilly. In 1739, he was enlisted as a founding governor of a new children's charity, the Foundling Hospital in Bloomsbury, London, which aimed to alleviate the problem of infants being abandoned by destitute mothers and which later became a centre for art and music.
During the Jacobite rising of 1745 the Duke raised a militia unit in support of the King known as the Derbyshire Blues, which mustered at the George Inn, Derby, on 3 December 1745.
On 27 March 1718, he married Catherine Hoskins (1700–1777), daughter of John Hoskins of Oxted (1640–1717) and Catherine Hale (1673–1703).
The Duke and Duchess had seven children: