The viridian metaltail (Metallura williami) is a species of hummingbird in the "coquettes", tribe Lesbiini of subfamily Lesbiinae.

Its throat, breast, and belly are mottled green and white and its outer tail feathers have whitish tips on their underside.

M. w. atrigularis has a black patch in the center of its gorget; its tail is slightly forked and its underside is shining green.

[6] The viridian metaltail is assumed to be sedentary, but males might disperse to the higher elevations outside the breeding season.

Nests are made of moss lined with soft plant down and small feathers, and are often placed in a rocky niche or other sheltered spot.

One vocalizatin of the viridian metaltail is "a descending series of 3–5 squeaky notes, often followed by several jumbled dry buzzy trills 'trsee-seee-seee-sew..trrk-tsetswe-trrk'".