Hochschild has been praised by scholars and critics for his narrative. Jeremy Harding, writing in The New York Times, called it "a model account" that showed how the human rights abuses and human rights activism that resulted became a "template for modernity". Richard F. Hamilton, writing in The Washington Post, called it an excellent book to counteract "the great forgetting" of the Congo atrocities.
However, Hochschild acknowledges that most of the facts illustrated in the book were already known (although appearing in works in several languages). Isidore Ndaywel è Nziem, a Congolese scholar whose Histoire générale du Congo was published the same year as King Leopold's Ghost, estimated the death toll in the Free State era and its aftermath at roughly 13 million (which Ndaywel è Nziem has subsequently revised downward to 10 million, a number similar to Hochschild's conclusion).
While Hochschild has said that his intention was to tell the story in "a way that brings characters alive, that brings out the moral dimension, that lays bare a great crime and a great crusade", he was criticised for his overly moralistic dimension, and former Belgian officials deplored his comparison of Leopold with Hitler and Stalin. Belgian historian Jean Stengers commented, "Terrible things happened, but Hochschild is exaggerating. It is absurd to say so many millions died." Hochschild was also criticized by Barbara Emerson, the author of a biography of Leopold, who described his book as "a very shoddy piece of work" and declared that "Leopold did not start a genocide. He was greedy for money and chose not to interest himself when things got out of control." Hochschild does not use the word genocide, but describes how the mass deaths happened as a result of the forced labor system instituted at Leopold's direction. Other historians have painted a picture similar to Hochschild's of the high death toll in Leopold's Congo, among them Jan Vansina, who appeared in the documentary based on the book, and the demographer Léon de Saint-Moulin. King Leopold's Ghost was specifically singled out for praise by the American Historical Association when it gave Hochschild its Theodore Roosevelt-Woodrow Wilson Award in 2008.