Indopithecus giganteus was originally named as a species of the European ape Dryopithecus, D. giganteus, by Guy Ellcock Pilgrim in 1915, based on a large lower third molar, holotype GSI-D175. However, George Edward Lewis in 1937 decided that Pilgrim's taxon was not congeneric with Dryopithecus and instead referred the molar to the co-eval ape Sivapithecus indicus.
Indopithecus giganteus was initially thought to be a member of the European ape genus Dryopithecus due to a single characteristic, a large lower third molar. However, further study by George Edward Lewis in 1937 led him to reassign it to the co-eval ape genus Sivapithecus.