The Red-legged Honeycreeper is on average 12.2 cm long, weighs 14 g and has a medium-long black, slightly decurved, bill. The male is violet-blue with black wings, tail and back, and bright red legs. The crown of its headis turquoise, and the underwing, visible only in flight, is lemon yellow. After the breeding season, the malemoults into an eclipse plumage, mainly greenish with black wings.
Females and immatures are mainly green, with paler, faintly streaked underparts. The legs are red-brown in the female, and brown in young birds.
The call of Red-legged Honeycreeper is a thin, high-pitched tsip.
Several subspecies are known. Differences are generally slight, with the Tobago race C. c. tobagensis being slightly larger than the mainland forms for example.
The Purplish Honeycreeper (Chlorophanes purpurascens), a bird from Venezuela known only from the type specimen, is considered to be an intergeneric hybrid between the Green Honeycreeper and either the Red-legged Honeycreeper or the Blue Dacnis.