The Marsh Seedeater (Sporophila palustris) is a species of bird in the Thraupidae family. It is sexually dichromic, with the males sporting a bright white throat, grey crown and chestnut belly, and the females resembling other brown female seedeaters.

It is found in Argentina, Brazil, Paraguay, and Uruguay. It is migratory, breeding in wet grasslands and marshes around Uruguay and Argentina and migrating northwards in the Austral winter to wet and dry grasslands in southern Brazil.

It is threatened by habitat loss, trapping for the pet trade, and pesticides. It is currently protected across most of its range and several protected areas may help safeguard this species.