Harcourt was private secretary to his father, Sir William, as Home Secretary from 1880 to 1885. He was Liberal Member of Parliament for Rossendale, Lancashire, from 1904 to 1916 and served as First Commissioner of Works in Sir Henry Campbell-Bannerman's 1905 ministry (appointed to Cabinet in 1907) and to H. H. Asquith's Cabinet between 1908 and 1910 and again between 1915 and 1916. In this role he authorised the placement in Kensington Gardens of the Peter Pan statue, sculpted by George Frampton, erected on 1 May 1912.