William Henry Cavendish-Scott-Bentinck, 4th Duke of Portland, PC (24 June 1768 – 27 March 1854), styled Marquess of Titchfield until 1809, was a British politician who served in various positions in the governments of George Canning and Lord Goderich.
Portland was the eldest son of Prime Minister William Cavendish-Bentinck, 3rd Duke of Portland and Lady Dorothy, daughter of William Cavendish, 4th Duke of Devonshire and Charlotte Boyle, Baroness Clifford. He was the elder brother of Lord William Bentinck and Lord Charles Bentinck.
He was educated first in Ealing under the tutelage of Samuel Goodenough graduating in 1774, followed by Westminster School (1783). He attended Christ Church, Oxford for two years but did not take a degree. The third Duke, who spared no expense for his heir, sent him to The Hague in 1786 for experience working with the crown's envoy, Sir James Harris. He returned in 1789.
He later received an honorary degree of Doctor of Civil Law from Oxford in 1793. He also served as a Family Trustee of the British Museum; in 1810, he loaned the famed Portland Vase to the museum.
Portland was Member of Parliament for Petersfield between 1790 and 1791 and for Buckinghamshire between 1791 and 1809.
He served under his father as a Lord of the Treasury between March and September 1807. He remained out of office until April 1827 when he was appointed Lord Privy Seal by his brother-in-law George Canning. He was sworn of the Privy Council the same year. When Lord Goderich became Prime Minister in August 1827, Portland became Lord President of the Council, an office he retained until the government fell in January 1828. Over time the Duke became less of a staunch Conservative, softening to some of the more liberal stances of Canning.
Portland also held the honorary post of Lord Lieutenant of Middlesex between 1794 and 1841.