Devonshire is a surprisingly distant figure. He was born William Cavendish in May 1720 in London, son of the Duke of Devonshire. But it is not known where he went to school.  He was known as the Marquess of Hartington, a courtesy title, from 1729.

He grew up as a committed Whig in a Whig family, and entered the family business in 1741 when he was elected MP for Derbyshire. He was initially a supporter of Robert Walpole and, after that, of Henry Pelham and the Duke of Newcastle.

He joined Pelham’s Cabinet as Master of the Horse, leaving the House of Commons at this time through writ of acceleration that allowed him into the House of Lords as Baron Cavendish. After Pelham’s death, Cavendish was appointed Lord Lieutenant of Ireland in April 1755.

He inherited his father’s title and became the Duke of Devonshire in December 1755.

Devonshire was quite successful at negotiating with the political factions in Ireland and was widely considered to have done a good job. Certainly, he had impressed William Pitt, who suggested to King George II that, after the collapse of Newcastle’s government, Devonshire be given a chance to take over. Devonshire, seeing it as a duty, said that he would only be in place until the end of the Parliamentary term.

A government was formed with Pitt as Southern Secretary, and the entire government was really nothing more than an internship for his leadership. The government dispatched forces to America, raised funds for the war, and established a militia.

Large amounts of the government’s attention were spent on the trial of Admiral Byng for failing to have properly reinforce Menorca when it was under attack from the French. Byng was found guilty and then shot by a firing squad in March. Pitt had protested, angering George II. The situation was compounded by George’s son the Duke of Cumberland refusing to take a military command while Pitt was in government. Finally, the King dismissed Pitt in April 1757.

Without Pitt’s popularity, and command of the Commons, the Devonshire ministry was effectively over, though the Duke continued as Prime Minister for a few more months until the Pitt-Newcastle ministry was formed in June.

Devonshire remained influential and was Lord Chamberlain in the Pitt-Newcastle ministry until 1762. However, George III disliked Devonshire; he was suspicious of the Whig aristocrats who had led the country since the Hanoverian succession. When Devonshire chose to resign from Cabinet, the King did not even meet him.

Devonshire married Charlotte Elizabeth Boyle in 1748. Though the marriage had been arranged in advance (and was highly advantageous, bringing Devonshire land in Yorkshire and Ireland, together with a selection of ‘pocket boroughs’), it turned out to be a happy one as well. They had four children. She predeceased him, dying in 1754.

Devonshire was only in his early forties but began to suffer from dropsy in 1763. He travelled to a Spa in the Austrian Netherlands (modern Belgium) for treatment and died there in October 1764 aged 44.