The blue-throated hummingbird is darkish green on the top of its body, blending to medium gray on its belly. It has a bright white stripe behind its eye and a narrower stripe reaching backward from the corner of its bill, bordering a blackish cheek patch. Its tail feathers are iridescent blue-black with broad white tips on the outer two to three pairs.
The species gets its name from the adult male's iridescent blue throat patch (gorget). The female does not have this. Instead it has a plain grey throat. Males sing two types of songs: a simple "peep song", which sounds like a squeaky wheel, and a quiet but hard "whisper song". The female is also thought to sing during the breeding season to attract males.