It resembles a small elegant Greenshank, with a long fine bill and very long yellowish legs. Like the Greenshank, it is greyish brown in breeding plumage, paler in winter, and has a white wedge up its back that is visible in flight.
However, it is more closely related to the Common Redshank and the Wood Sandpiper (Pereira and Baker, 2005). Together, they form a group of smallish shanks that tend to have red or reddish legs, and in breeding plumage are generally a subdued, light brown above with some darker mottling, with a pattern of somewhat diffuse small brownish spots on the breast and neck.
It is a migratory species, with the majority of birds wintering in Africa, and India with fewer migrating to Southeast Asia and Australia. They prefer to winter on freshwater wetlands such as swamps and lakes and are usually seen singly or in small groups.
The Marsh Sandpiper birds forage by probing in shallow water or on wet mud. They mainly eat insects and similar small prey.
The Marsh Sandpiper is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.