The great-billed seed finch (Sporophila maximiliani) is a species of bird in the family Thraupidae. Its natural habitats are subtropical or tropical moist shrubland, swamps, and heavily degraded former forest. They are found in two separate general populations, one in the northern Amazon rainforest and the other in the Cerrado. They live in flooded areas with nests low to the ground. The adults express strong sexual dimorphism. Males are black with white under wing-coverts and ivory white bills, and the females are generally light brown with white under wing-coverts and black bills. Both the male and female have very large, thick bills. The great-billed seed finch has a melodious call, which has made it a target for trapping. Although the population is quickly declining due to trapping and loss of habitat, not much is known about its behavior and ecology. The great-billed seed finch exists in two separate populations in South America. The southern population is found in the Cerrado and in the Cerrado enclaves into the transition zones in Atlantic Forest. The northern population is found in the northern Amazon rainforest.

The great-billed seed finch is specialized to live in humid environments and is often associated with flooded areas and marshy borders.