William Cavendish, 3rd Duke of Devonshire, KG, PC (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.

He served as Lord Privy Seal from 1731 to 1733, when he was invested as a Knight of the Garter.

[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.