[3][4] The vervain hummingbird was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Trochilus minimus.

[5] Linnaeus based his description on a bird that had been described and illustrated in 1747 by the English naturalist George Edwards.

[8][3] Two subspecies of vervain hummingbird are recognised, the nominate M. m. minima (Linnaeus, 1758) and M. m. vielloti (Shaw, 1812).

[9][10] Males have dull metallic green uppersides that are almost black on the rump and uppertail coverts.

[11] The species inhabits almost every available landscape throughout its range except the interior of dense montane forest.

[10] The vervain hummingbird does not migrate in the conventional sense but appears to make elevational movements in response to food availability.

The female makes a tiny cup nest of soft material such as hair and plant down covered with lichen or moss; it is held together and anchored to a branch with spiderweb.

The clutch is two eggs that are among the smallest of all birds', with an average length of 1 cm (0.39 in) and weighing about 0.38 g (0.013 oz).

The sing during most of the day from exposed perches in their territory and also during the courtship display and during encounters with other males.