The Sooty Myzomela is a small honeyeater about 11–12 cm long. It is active in forest by day and feeds mainly on nectar, also taking small insects and fruit.
It is about 11–12 cm long and weighs about 14.4–14.5 g.
It is sedentary and diurnal in forest, feeding in the canopy of tall trees on nectar, small insects and occasionally small fruit.
In surveys in 2012 and 2013, it was uncommon in coastal mangroves and coconut habitat on Makira, but abundant in similar seaside habitat on Santa Catalina.
The black back has a faint violet-blue sheen, and the flight feathers are tinged brown. The black bill curves downward. Juveniles are duller, with sooty-black upperparts and greyish-olive underparts.
An extinction-risk assessment has not been added yet.