Several studies have reported the occurrence of fossil remains of a now extinct Boa snake from the upper Pleistocene of Marie-Galante Island, French West Indies. However, these remains have never been fully investigated and no complete description of this possible new species has been published. In this paper, we try to bridge this gap by providing a detailed morphological study of the Boa remains discovered in the three major fossil deposits of Marie-Galante Island. Our study reveals the specific morphological aspects of this fossil snake and allows us to identify it as a new species, Boa blanchardensis. We also reconstructed its body size, carried out a paleohistological investigation, and suggest that this snake may have been a dwarf species. We then discuss the possible explanation for the extinction of this snake on Marie-Galante Island and possibly also on other Guadeloupe islands.