Tagiades japetus has dark brown upperwings, on the forewings there are white hyalin patches in spaces 3, 6, 7 and 8 respectively in both sexes, spots in spaces 4 and 5 in females only. Larger and clearer patches in females than males. There is a dark brown discal / post-discal spot in space 1b and 8 cells of the forewing, in addition to that on the hindwing there is also a smaller post-discal spot in spaces 1b and 6. The underside of the wings is pale yellowish brown with the same markings like its upper side, its hindwings are covered with white scalling.
Larva: larvae of Tagiades japetus have a cylindrical body, pale yellow in color with a reddish lateral band along the body, a black head capsule and dark brown or black collar markings on the back of the prothorax. At the next instar, the body of the caterpillar turns green, its lateral band begins to disappear, yellow spots adorn the surface of the body and its head capsule is reddish brown in color.
Pupa: Tagiades japetus pupae are pale cream brown in color with two large white patches on the wingbox and ventral segment. This species has a pupa with a short thorax, a long abdomen and a tapered rostrum