Dynastes neptunus occurs in the Andes mountains of northwest South America, in Venezuela, Colombia, Ecuador and Peru.
Its habitat is the lush and humid montane tropical forest, sometimes called ‘cloudforest’.
Little is known about its distribution but it occurs most often above 700 m elevation, up to at least 2500 m in suitable areas.
The species is apparently present on both the western and the eastern slopes of the Andes.
The larvae of the beetle develop in the decomposing wood of large trees, especially standing dead trees.
Therefore the survival of the species is entirely dependent on the availability of such trees which are only found in primary or mature secondary forest areas that have not been deforested.