Female and juvenile Redheads are brownish-grey overall, with grey legs, black eyes and a grey bill with a black tip. Males in breeding plumage have a grey body, black rump and breast, and a bright rufous head with a yellow eye and a light blue bill with a black tip. The male in non-breeding plumage (from July to September) is overall dark brown, but still has a dull reddish head. Redheads are a little smaller than the similar looking Canvasbacks, with a rounder head, a lighter back, and a more typically duck-shaped bill.  Redheads nest on marshy freshwater lakes, ponds, slow moving rivers and other wetlands in prairie zones. During migration they gather on large lakes and they spend the winter on sheltered saltwater bays and estuaries and some inland lakes.

Redheads usually gather in small flocks, often mixed with other diving duck species. But in the winter they congregate in very large flocks, made up of tens of thousands of birds. Although they are considered divers, they often feed by dabbling. A notable behaviour of the Redhead is their tendency to parasitize, or lay eggs in other duck's nests. Many ducks will lay eggs in each other’s nests, but the Redhead takes this practice to another level. Female Redheads regularly parasitize each other, and at least ten other species of duck, and some non-duck species as well. Most females parasitize in addition to raising their own brood, but some females may be entirely parasitic, not raising their own brood at all. Sometimes, dump nests occur that are untended and never incubated, but may have up to 87 eggs in them.

Nests are located close together in dense marshes, especially areas with dense bulrush, above shallow water or on dry land. The female builds a bulky bowl out of vegetation and, if it is in water, anchors it to some emergent vegetation. The nest is then lined with down. Actual clutch size is difficult to determine due to the Redhead's parasitism, but clutch size usually ranges between 6-14 eggs. The female incubates for about 23-29 days, during which time, the male leaves. About a day after hatching, the female leads the young away from the nest to water, where they feed themselves. The young are capable of flight after 60-65 days.