Small for a songbird, with a thin, pointed bill and long black legs. They can be identified by their olive green and bright yellow feathers on their head and back, and black-and-white wings. Males have black throats and gray underbelly plumage; females have lighter coloring on their throats and black markings on their chest. 

Around 4.3–4.7 inches (11–12 centimeters) long. They weigh between 0.3–0.4 ounces (8.5–11.3 grams), about the same weight as two nickels.

Deep inside northern forests with a mix of coniferous and broad-leafed trees. They make migratory stops in wooded areas and winter among mountain forests.

The oldest bird on record lived for about 6 years, lifespan otherwise unknown.

Males sing to establish their territory and attract females during the breeding season. 

Black-throated green warblers fly quickly among the trees in search of insects to eat, often hovering to pluck their prey from the undersides of leaves. They also eat berries sometimes.

Black-throated green warblers are active during the daytime, but they are nighttime migrants.

Males are the first to arrive at the forest breeding grounds, claiming their territory through song and by repelling other males until the females arrive a week later. Males and females work together to build cup-shaped nests made from twigs and grasses, usually in conifer trees and often fairly close to the ground. Females lay three to five eggs per clutch, which are incubated for about two weeks before hatching. Both parents, but mostly the mother, feed the babies right after hatching. Once the babies grow feathers, the parents are rarely seen together, each one splitting up care for half of the fledglings until they are ready to leave the nest after a month.

These birds migrate in the nighttime, so they are at risk for collisions with reflective buildings, telephone towers, and other man-made structures. Also, parts of their northeastern breeding grounds are threatened by deforestation and habitat loss.