Miller's mastiff bat occurs from Central America into northern South America. It forages in open areas such as grassland and dry woodland, and records describe roosts in caves, buildings, and hollow trees.
The back is black to blackish and the underside is somewhat paler. Older fur may appear reddish brown; this change should not be mistaken for a separate color morph.
It uses open habitats such as grassland savannas and dry woodland. Roost records include caves, a church roof, and a hollow tree. Fecal samples contained moth scales and parts of beetles.
An extinction-risk assessment has not been added yet.