Adult Boat-billed Flycatchers have black heads with a strong white eyestripe and a concealed yellow crown stripe. The upperparts are olive-brown, and the wings and tail are brown with only faint rufous fringes. The underparts are yellow, and the throat is white.
Boat-billed Flycatchers wait on a concealed perch high in a tree and sally out to catch insects in flight. They will also take invertebrates off the foliage and eat some berries.