Adults of both sexes have deep metallic grass green upperparts with some bronze on the rump and black uppertail coverts.

[6] Adult females have a buff chin and throat and grayish white underparts with metallic green on the sides of the breast.

It inhabits the interior and edges of humid evergreen and pine-oak forest and also the transition zone from the latter into cloudforest.

[6] The green-breasted mountaingem feeds on nectar and small insects and spiders, but details of it diet and foraging techniques are lacking.

[6] The IUCN has assessed the green-breasted mountaingem as being of Least Concern, though its population size is unknown and believed to be decreasing.

[1] "[A]ppropriate habitat in the Green-breasted Mountain-gem’s small and patchy distribution is likely to further decrease in size" due to global warming.