He took this opportunity to resume his parliamentary career, being elected to the constituency of Tregony on 5 April 1784, holding the seat until 1790. He does not appear to have ever spoken in parliament, but records show that he voted in favour of William Pitt over his 1785 Reform Bill, against him during the Regency crises of 1788 and 1789, and against the Duke of Richmond's fortification plans in 1786. The Nootka Crisis in 1790 brought an end to his career in politics, as Kingsmill returned to active duty in command of the 90-gun . The crisis passed without breaking into open war, and Kingsmill paid off "Duke" and once again entered semi-retirement. In October 1790, he was selected to serve as a member of the panel of officers at the court-martial concerning the mutiny and loss of . As contemporaries in the service, Sir Robert and Horatio Nelson developed a close friendship that lasted until Nelson's death at Trafalgar on 21 October 1805.