William Henry Cavendish Cavendish-Bentinck, 3rd Duke of Portland (14 April 1738 – 30 October 1809) was a British Whig and Tory statesman, Chancellor of the University of Oxford, Prime Minister of Great Britain, serving in 1783 and Prime Minister of the United Kingdom from 1807 to 1809. The 24 years between his two terms as Prime Minister is the longest gap between terms of office of any Prime Minister. He was known before 1762 by the courtesy title Marquess of Titchfield. He held a title of every degree of British nobility—Duke, Marquess, Earl, Viscount, and Baron. He is also a great-great-great-grandfather of Queen Elizabeth II through her maternal grandmother.
He was elected to sit in the Parliament for Weobley in 1761 before entering the Lords when he succeeded his father as Duke of Portland the next year. Associated with the aristocratic Whig party of Lord Rockingham, Portland served as Lord Chamberlain of the Household in Rockingham's first Government (1765–1766) and then as Lord Lieutenant of Ireland in Rockingham's second ministry (April–August 1782); he resigned from Lord Shelburne's ministry along with other supporters of Charles James Fox following Rockingham's death.[5]
In April 1783, Portland was brought forward as titular head of a coalition government as Prime Minister, whose real leaders were Charles James Fox and Lord North. He served as First Lord of the Treasury in this ministry until its fall in December of the same year. During his tenure the Treaty of Paris was signed formally ending the American Revolutionary War.
In 1789, Portland became one of several vice presidents of London's Foundling Hospital. This charity had become one of the most fashionable of the time, with several notables serving on its board. At its creation, fifty years earlier, Portland's father, William Bentinck, 2nd Duke of Portland, had been one of the founding governors, listed on the charity's royal charter granted by George II. The hospital's mission was to care for the abandoned children in London; and it achieved rapid fame through its poignant mission, its art collection donated from supporting artists, and popular benefit concerts put on by George Frideric Handel. In 1793, Portland took over the presidency of the charity from Lord North.
Along with many conservative Whigs such as Edmund Burke, Portland was deeply uncomfortable with the French Revolution and broke with Fox over this issue, joining Pitt's government as Home Secretary in 1794. He continued to serve in the cabinet until Pitt's death in 1806—from 1801 to 1805 as Lord President of the Council and then as a Minister without Portfolio.
In March 1807, after the collapse of the Ministry of all the Talents, Pitt's supporters returned to power; and Portland was, once again, an acceptable figurehead for a fractious group of ministers that included George Canning, Lord Castlereagh, Lord Hawkesbury, and Spencer Perceval.
Portland's second government saw the United Kingdom's complete isolation on the continent but also the beginning of recovery, with the start of the Peninsular War. In late 1809, with Portland's health poor and the ministry rocked by the scandalous duel between Canning and Castlereagh, Portland resigned, dying shortly thereafter.
He was Recorder of Nottingham until his death in 1809.