Red-billed quelea closely related to the fodies ("Foudia"), a genus of six or seven species that occur on the islands of the western Indian Ocean. These two genera are in turn the sister clade to the Asian species of the genus "Ploceus". The following tree represents current insight of the relationships between the species of "Quelea", and their closest relatives. Interbreeding between red-billed and red-headed queleas has been observed in captivity. The red-billed quelea is a small sparrow-like bird, approximately long and weighing , with a heavy, cone-shaped bill, which is red (in females outside the breeding season and males) or orange
Red-billed quelea and wing coverts and flight feathers have buff margins. At an age of about five months they moult again and their plumage starts to look like that of breeding adults, with a pinkish-purple bill. Different subspecies are distinguished by different colour patterns of the male breeding plumage. In the typical subspecies, "Q. quelea quelea", breeding males have a buff crown, nape and underparts and the black mask extends high up the forehead. In " Q. quelea lathamii" the mask also extends high up the forehead, but the underparts are mainly white. In "Q. quelea aethiopica" the mask does not extend