Hochschild has been praised by critics for his narrative. However, he acknowledges that most of the facts illustrated in the book were already known (although appearing in works in several languages). The book was praised by scholars of Africa such as Prof. Robert Harms of Yale University and by the South African Nobel laureate Nadine Gordimer.
Belgian historian Jules Marchal called the book "a masterpiece, without even one error about the historical deeds related." Several other Belgian experts on the period, such as anthropologist Jan Vansina, have also voiced support for Hochschild. 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, a higher figure than the various estimates cited by Hochschild.
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.
The Belgian historian Jean Stengers, whose works are cited in King Leopold's Ghost, argued in a newspaper article that Hochschild's moral judgements were "not justified in respect to the time and place" and that his conclusions about the scale of the mass murder were based on incomplete statistics. He argued that, in Hochschild's book, historical objectivity was affected by the desire to attract a wide public. Hochschild replied to Stengers' criticism, accusing him of not accepting the implications of his own research, arguing that while Stengers was "a meticulous and talented scholar", he was affected by colonialist bias. Hochschild points out that the estimates about the reduction of the population of the Congo reported in his book are taken in part from Stengers' writings.
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.