Culms 1-2.5 m; nodes 7-12. Blades 10-25 mm wide. Panicles 10-20 cm, producing around 4,000-6,000 caryopses; lower branches about 3 cm, producing a lobed appearance. Spikelets morphologically indistinguishable from those of var. viridis. 2n = 18.
Setaria viridis var. major is a major adventive weed in corn and bean fields of the midwestern United States, dwarfing var. viridis in stature.