The white-headed munia is a small bird measuring 11 cm in length and weighing about 11 grams. Adult birds have chestnut brown upperparts, flanks and wings, an entirely white head, throat and upper breast which is tinged with buff. The tail is black-brown and the belly is black. The bill and legs are light grey.

There is very subtle sexual dimorphism in adult birds, with the head of the male being whiter than that of the female, and getting whiter with age. This often causes young male birds to be confused with females. Additionally the definition line between the breast and the flanks is more pronounced in the male.

This species is often confused with, and referred to as, the pale-headed munia (Lonchura pallida) which can be differentiated by tan coloured flanks which are lighter than the brown wings and also by the absence of the black belly.

Juvenile birds are more cinnamon coloured above with a buff face and underparts, a brown iris, grey bill and blue-grey feet. They are practically impossible to differentiate from juveniles of other species such as white-capped munia (Lonchura ferruginosa), pale-headed munia (Lonchura pallida), chestnut munia (Lonchura atricapilla) or scaly-breasted munia (Lonchura punctulata).