Red-berried elderberry is a shrub or small tree up to 24 feet tall, not forming colonies.
Leaves are opposite, compound, 3–7 inches long with 5–7 leaflets; leaflets 2–4 inches long, ¾–1¼ inches wide, broadly lance-shaped to broadest below the middle, blades often with uneven sides; margin sharply toothed; upper surface dark green; lower surface paler, hairy at first, smooth later. End leaflet stalk is ¼–1 inch long, while the side leaflet stalks are short or absent.
Twigs are hairy when young, gray to reddish brown or yellowish brown; smooth later. Pores are prominent. Bark on trunk is tight, greenish brown or grayish brown, smooth; pores raised. Wood soft; a narrow ring of soft greenish-white material around the brown pith.
Flowering is in April–May. Flowers are white, about 1/8 inch across, in dense egg-shaped or pyramidal clusters 2–4 inches long, 1¼–2 inches wide, with usually only 1 elongated main stalk; petals 5.
Fruits mature June–August. Fruits are red, semiglossy, berrylike, egg-shaped, about 1/8 inch across, in pyramidal clusters up to 4 inches long. Juice yellowish. Fruits are unpalatable, with an unpleasant flavor. Seeds 3 per fruit.