In the revised classification to create monophyletic genera, the white-bellied hummingbird was placed by most taxonomic systems in a new genus Elliotomyia.

Both sexes of both subspecies have a medium length straight bill with a blackish maxilla and a reddish mandible with a dark tip.

Adult males of the nominate subspecies have brilliant light green upperparts, sides, and chest.

Adult females are very similar to males, but with a light cream chin and throat that are more heavily spotted.

[11] The nominate subspecies of white-bellied hummingbird is found on the east slope of the Peruvian Andes between the departments of Amazonas and Cuzco.

[11] The white-bellied hummingbird forages for nectar at a wide variety of flowering plants, shrubs, and trees.

It makes a cup nest of plant wool and moss with lichens on the outside and typically places it in a shrub or small tree between 2 and 5 m (7 and 20 ft) above the ground.

The song of the nominate white-bellied hummingbird subspecies is "a repeated short phrase typically comprising three squeaky notes, 'tseet-chew-chip … tseet-chew-chip …'."