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.
Family
Portland married Henrietta, eldest daughter and heiress of Major-General John Scott of Fife and his wife Margaret, in London on 4 August 1795. At the time of his marriage he obtained Royal Licence to take the name and arms of Scott in addition to that of Cavendish-Bentinck. They were parents of nine children:
William Henry, Marquess of Titchfield
Lady Margaret Harriet
Lady Caroline
William Cavendish-Scott-Bentinck, Marquess of Titchfield, later 5th Duke of Portland
The Duchess of Portland died on 24 April 1844. Nearly 10 years later, Portland died at the family seat of Welbeck Abbey, Nottinghamshire, in March 1854, aged 85. Two of their sons predeceased their parents; their eldest dying of a brain lesion and their third son dying of a heart attack. The duke expressed a desire to be buried in the open churchyard in Bolsover, Derbyshire, near the other family seat at Bolsover Castle. However, he was instead interred in the ancient Cavendish vault, that had previously been unopened for 138 years. He was succeeded in the dukedom by his second son, William. The department of Manuscripts and Special Collections, The University of Nottingham holds a number of papers relating to Portland: His personal and political papers are part of the Portland Collection while the Portland Collection contains papers relating to his estate business. The Portland Estate Papers held at Nottinghamshire Archives also contain items relating to Portland's properties.
Arms
Titles
His full titles were Duke of Portland, Marquess of Titchfield, Earl of Portland, Viscount Woodstock, and Baron Cirencester.
The Most Honourable William Cavendish-Bentinck, Marquess of Titchfield