Male: There is sexual dimorphism in this species. The wings are long with angular apices. They are iridescent bluish-green with a black central band. There is a pronounced sex brand. The underside is green or blue-green with black veins. Males are smaller than females. The abdomen is bright yellow. The wingspan of the males is approximately 20 cm, but more usually about 16 cm. A spectacular form of the male is form atavus, which has gold spots on the hind wings.
Female: Female Queen Alexandra's Birdwings are larger than males with markedly rounder, broader wings. The female can reach, and slightly exceed, a wingspan of 25 cm, a body length of 8 cm and a body mass of up to 12 grams, all enormous measurements for a butterfly. The female has brown wings with white markings arranged as two rows of chevrons. The hindwings are brown with a submarginal line of centered yellow triangles. The body is cream-coloured and there is a small section of red fur on the brown thorax.