Its plumage is black, and it has a sheen which is glossy and iridescent. The female is smaller and duller than the male. The bills of both sexes are long, sharp and black. The average length of the common grackle is 28-34 cm. The adults' eyes are yellow.
Juveniles have brown plumage and brown eyes.
During breeding, the diet of the common grackle consists mainly of insects and other invertebrates. The diet may also include goldfish, minnows, crayfish, small frogs, salamanders, mice, and bats, which are caught from the air. During migration and the winter periods, agricultural grains and seeds dominate the diet, particularly corn and acorns. Some fruits are also consumed. Adults have been observed snatching earthworms from feeding robins.