Portland was born William Henry, Lord Titchfield in April 1738 into an aristocratic family at Bulstrode Park in Buckinghamshire. He was educated at Westminster School and Christ Church, Oxford.

He was briefly MP for the seat of Weobley in 1761 but was elevated to the House of Lords upon the death of his father the following year. He inherited large estates, and a substantial fortune, of which he would spend much on politics.

Painfully shy, Portland rarely spoke in the House of Lords, even during his spells as Prime Minister. But Portland, who associated with the Whig faction, was a duke, was wealthy and was apparently willing to contribute a great deal of time to politics. He later became a strong ally of Charles James Fox, though the men disagreed on how far reform should go.

In 1765, Portland joined Rockingham’s short-lived government as Lord Chamberlain. He returned to opposition for 16 years after Rockingham’s fall. In 1782, Rockingham returned as Prime Minister, and Portland was appointed Lord Lieutenant of Ireland, for three months, before Rockingham’s death ended the government. Portland soon resigned from Shelburne’s government.

When Shelburne fell, the King was presented with an alliance of the Whig Charles James Fox and the Tory former Prime Minister Lord North. It was a powerful, if odd, political pairing, and required a third person to be leader, with both men requesting Portland.

Portland duly became Prime Minister in April 1783. But George III disliked the arrangement, and plotted with Pitt to bring the government down. Eventually, after the government lost a vote on an India Bill (mainly due to pressure from the King), George III dismissed the Portland government in December after 160 days.

Like many of his class, Portland was initially excited by the French Revolution, but as the violence in Paris escalated, he became more worried. In 1794, he joined Pitt’s government as Home Secretary, bringing with him several conservative Whigs, splitting the parliamentary group.

From 1794 to 1801, Portland served as Home Secretary. It was a crucial time, when discontent from the French Revolution inspired radicals in Britain, while the strains of war required a firm hand. He also played an important role in the union with Ireland, making funds available to smooth things over with Irish legislators who voted for the union. He carried on in government as Lord President of the Council under Addington

In 1807, after the fall of Grenville, George III asked the elderly Portland to step in. Portland was concerned that his health would not permit an effective government (he had received an operation for kidney stones the previous year), but he accepted out of loyalty to George.

His government was not especially successful, and Portland found Cabinet, which he rarely bothered to attend, dominated by the powerful personalities of Canning, Castlereagh, Hawkesbury, and Perceval. Without any firm direction from Portland the government degenerated into scheming and recrimination.

Portland resigned in October 1809 after a stroke. He had been Prime Minister for two years and 187 days.

At some point in his life, Portland held a title for every degree of British nobility: duke, marquess, earl, viscount, and baron. The gap in his two premierships is the longest of any Prime Minister. He is also King Charles III’s great-grandfather. He was also the Chancellor of Oxford University from 1792 and the President of the Foundling Hospital in London from 1793, holding both positions until his death.

Portland married Lady Dorothy Cavendish in 1766 and they had six children, five of whom reached adulthood. She died in 1794.

Portland died on 30 October 1809, just 26 days after leaving office.