The adult Eastern meadowlark measures from 19 to 28 cm (7.5 to 11 in) in length and spans 35–40 cm (14–16 in) across the wings. Body mass ranges from 76 to 150 g (2.7 to 5.3 oz). The extended wing bone measures 8.9–12.9 cm (3.5–5.1 in), the tail measures 5.3–8.6 cm (2.1–3.4 in), the culmen measures 2.8–3.7 cm (1.1–1.5 in) and the tarsus measures 3.6–4.7 cm (1.4–1.9 in). Females are smaller in all physicial dimensions. Adults have yellow underparts with a black "V" on the breast and white flanks with black streaks. The upperparts are mainly brown with black streaks. They have a long pointed bill; the head is striped with light brown and black.
The song of this bird is of pure, melancholy whistles, and thus simpler than the jumbled and flutey song of the Western Meadowlark; their ranges overlap across central North America. In the field, the song is often the easiest way to tell the two species apart, though plumage differences do exist, like tail pattern and malar coloration.
The pale Lilian's Meadowlark of northern Mexico and the southwestern US is sometimes split off as a separate species.