The white-banded swallow is a medium-sized swallow, measuring, on average, and weighing . They usually have a wingspan of . They decline in size from north to south, but this is a gradual decline, which suggests that there is no geographical variation. It is black, except for the band on its breast, its thighs, and bars on the edge of its wings, which are all white. It also has blackish-brown underwing coverts. Their feathers have a blue-black luster. This swallow has a deeply forked tail. The sexes are similar, although the females weigh slightly more on average ( for the males, for the females). The juveniles are noted to be duller and browner, with shorter and paler feathers.