The breeding season of square-tailed kites is specific to the location of the birds. Those in temperate Australia will breed between July and February, while those in more tropical areas will breed around April. When nesting, square-tailed kites prefer large, tall trees in uncleared areas. Both the male and female birds will participate in the building of the nest, or will add to disused nests of other species. Nest shape will either be the typical bowl-shaped nest, or a stick platform, and construction of the nest usually takes around 3 weeks. During the breeding season the female will roost on the nest at night, while the male roosts in a nearby tree, and when young are present both the male and female will roost near the nest. Only one attempt to breed is made each season, with a clutch producing 1–2 white eggs that are a round to oval shape. The incubation period for this species is around 40 days and offspring care is biparental. Incubation of the eggs is primarily done by the female, as the male hunts and brings food to the nest, however males have also been seen incubating eggs. The nestling stage lasts about 8 weeks, with an additional two months of dependence post-fledging. On hatching, offspring is semi-altricial with feathers and vocalisations developed by 3 weeks, post hatching.
