He married on 1 July,1899 Mary Ethel Burns, daughter of Walter Hayes Burns, of New York and North Mymms Park, Hertfordshire. They had a son, William, in 1908.
He was Liberal MP for Rossendale, Lancashire, 1904-1916.
He was First Commissioner of Works in Sir Henry Campbell-Bannerman's 1905 ministry (included in the cabinet in 1907) and in Asquith's cabinet 1908-10 and again 1915-16. In this role he authorised the placement in Kensington Gardens of the Peter Pan statue, sculpted by George Frampton, erected on May 1, 1912. He was Secretary of State for the Colonies 1910-15.
Harcourt received an honorary DCL degree from Oxford University, and was created the first Viscount Harcourt, of Stanton Harcourt, Oxon, on 3 January, 1917.
Port Harcourt, capital of Rivers state in southern Nigeria, is named after him. When the port was established in 1912, there was much controversy about the name it should receive. In August 1913, the Governor–General of Nigeria, Sir Frederick Lugard wrote to Harcourt, then Secretary of State for the Colonies, "in the absence of any convenient local name, I would respectfully ask your permission to call this Port Harcourt." To this the Secretary of State replied "It gives me pleasure to accede to your suggestion that my name should be associated with the new Port."
Harcourt's diaries contain a report that one of Queen Victoria's chaplains, Rev'd Norman Macleod, made a deathbed confession to Harcourt repenting of his action in presiding over Queen Victoria's marriage to her servant, John Brown. Some scholars doubt the veracity of Harcourt's account and question why a royal chaplain would confess to a politician. Others are equally certain that Victoria was in love with Brown and regard Harcourt's account as confirmation that a marriage actually occured. Supporters of the Brown marriage theory regard Harcourt as a well-placed source with no obvious reason to place a false story in his private diaries.