[3] Though one mid-late twentieth century publication credited Lichtenstein with the species description, since the 1990s taxonomic systems attribute it to Deppe.

Adults have a dull olive crown with minimal or no white in the middle.

Their throat is dull gray, their breast olive in a vest-like pattern, their belly white, and their flanks and undertail coverts whitish with a yellow wash.

Though the species is a year-round resident in much of its range there appears to be a northward shift during the austral winter.

[8] The olivaceous elaenia's breeding season appears to span from September to April.

Its nest is a cup made from moss, plant fibers, and fungal haphae with lichens on the outside.

The olivaceous elaenia's primary vocalization is a "clapping 'Vrih' or 'Vri-der', single or in series".