The Fiery-throated Hummingbird averages 11 cm or 4.3 inches in length and weighs about 5.7 g or 0.2 oz. It has a straight black bill and dusky-colored feet.
The adult Fiery-throated Hummingbird has iridescent green body plumage, a dark blue tail, and a white spot behind each eye. It has a brilliant blue crown, yellow-bordered coppery orange throat, and blue chest patch. Its sides and the back of the head are velvety black.