Harcourt was promoted to full general on 1 January 1798 and he became the first Governor of the Royal Military College at Great Marlow in June 1801. Appointed a Deputy Lieutenant of Berkshire in November 1801, he succeeded his elder brother, George Simon Harcourt, 2nd Earl Harcourt, to the earldom in April 1809 and was appointed Governor of Portsmouth in July 1811. Appointed a Knight Grand Cross of the Order of the Bath on 20 May 1820 and promoted to field marshal on 17 July 1821, Harcourt bore the Union standard at the coronation of George IV on 19 July 1821. He went on to become Governor of Plymouth in 1827.