It is active throughout the year and is primarily nocturnal. The house rests on a base of decaying vegetation and is composed of tightly woven grass or emergent aquatic plants. In the middle of the house is a nest chamber about 100 mm in diameter, and there are usually two exits leading downward in opposite directions from the chamber. A network of surface trails about 75 mm wide entwine the vegetation near the house and lead into the water. Before giving birth, a female will thicken the walls and raise the floor of her house.
Some individuals dig burrows near a marsh and also burrow into the marsh bottom during a drought.
From one to six floating feeding platforms 100-150 mm in diameter and containing one or two plunge holes are located above the water near the house. Sometimes a protective cover is added to a platform. The round-tailed muskrat is entirely herbivorous. It also eats rushes, sedges, sawgrass, and mangrove bark. Food may be consumed where it is found, carried to a feeding platform, or brought back to the nest.