This little bird is native to Canada, Mexico, and the United States. Their breeding habitat is marshes with tall vegetation such as cattails across North America. In the western United States, some birds are permanent residents. Other birds migrate to marshes and salt marshes in the southern United States and Mexico. their non-breeding range is in the southern United States going into Mexico and their breeding range is in the northeastern United States going into Canada.
These birds forage actively in vegetation, sometimes flying up to catch insects in flight. They mainly eat insects, also spiders and snails.
The nest is an oval lump attached to marsh vegetation, entered from the side. The clutch is normally four to six eggs, though the number can range from three to ten. The male builds many unused nests in his territory. A hypothesis of the possible reason to why males build multiple "dummy" nests in their territory is that they are courting areas and that the females construct the "breeding nest", where she lays the eggs in. He may puncture the eggs and fatally peck the nestlings of other birds nesting nearby, including his own species (even his own offspring) and red-winged blackbirds, yellow-headed blackbirds, and least bitterns. Marsh wren young can get infected by pathogenic larvae. The Blowfly larvae infect the young by subdermal myiasis-induced lesions and subsequent sepsis. The larvae form a wound in the young by rasping and expanding a hole in their skin to create blood flow and feed on the blood of the hosts' body. This bird is still common, although its numbers have declined with the loss of suitable wetland habitat. Wholesale draining of marshes will lead to local extinction. Still, this species is widespread enough not to qualify as threatened according to the IUCN.