His father William Henry Cavendish-Scott-Bentinck, was the 4th Duke of Portland. His sister Charlotte Denison, was the Viscountess Ossington.
Although he was M.P for King's Lynn from 1824-1826 he took no active part in politics, allowing three years to pass between his succeeding to the dukedom and first taking his seat in the House of Lords. He did, however, have a wide-ranging network of family and friends with whom he maintained an extensive correspondence. He undertook major developments at Welbeck, and was actively involved in the management of the Portland estates, both of which activities are reflected in his papers.