The Tsavo sunbird is 9.5 to 10 cm (3.75 to 4 inches) long. The bill is down-curved and rather short for a sunbird, especially compared to that of the otherwise similar Marico sunbird.
The female is greyish-brown above and on the head with a white eyebrow stripe; the throat is either white or dusky with white edges (malar strips). The underparts are faintly yellow-tinged white with dusky stripes on the breast. The tail is bluish-black with grey edges and tip.
The juvenile male looks like the dark-throated form of the female. Later it develops a black throat and black wing coverts, both with green feathers intermixed, and often a wide black stripe down the belly.
The adult male is apparently the same at all seasons: gleaming bluish-green above and on the head, with a black belly and lower breast. The upper breast may have a maroon band, missing the center or complete and 3 to 5 mm wide. (The male purple-banded sunbird has a wider maroon band and a distinct non-breeding plumage.)
The song is "a rapid sputtering tsustiseesee, chuchiti-tsi-tsi-tsi-tsi sitisee-see-see-see chitisee… " and variants, sometimes only the last few notes. Calls resemble the purple-banded sunbird's: "oud annoyance chatter, chi-chi-chi-chi… " and "a high tsik-tsiki-tsik or brrrzi. "
It is found in the Tsavo region of southeastern Kenya and nearby northern Tanzania, but not on the coast. It lives in arid scrub with Commiphora and Acacia trees and shrubs.