The species lives in open or semiopen country, and often travels in flocks, sometimes mixed with red-winged blackbirds (particularly in spring) and bobolinks (particularly in fall), as well as common grackles or European starlings.[2] These birds forage on the ground, often following grazing animals such as horses and cattle to catch insects stirred up by the larger animals. They mainly eat seeds and insects.

Before European settlement, brown-headed cowbirds followed bison herds across the prairies. Their population expanded with the clearing of forested areas and the introduction of new grazing animals by settlers across North America. They are now commonly seen at suburban birdfeeders.

The brown-headed cowbird is an obligate brood parasite; it lays its eggs in the nests of other small passerines (perching birds), particularly those that build cup-like nests. The brown-headed cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors.[12][13] The young cowbird is fed by the host parents at the expense of their own young. Brown-headed cowbird females can lay up to 36 eggs in a season. More than 140 different species of birds are known to have raised young cowbirds.[14]