The breeding season is shorter and more consistent than other species of ibis, beginning two months after the rainy season begins (Hancock et al. 1992). Breeding has been reported in February-April in Colombia and Panama, in September in Suriname, and in June-August in Venezuela (Hancock et al. 1992).
A Green Ibis pair built a nest on the same branch as a pair of Sunbittern (Eurypyga helias), only 18 days after the Sunbittern chick fledged and the parents had left (Thomas and Strahl 1990). The nest is a platform of loosely placed sticks, with a diameter of ca 0.5 m, and contained one or two chicks one month after construction (Thomas and Strahl 1990). The eggs are deep olive-green, most often without markings, but sometimes with fine brown or blackish spots or irregular lines at the larger end (Wetmore 1965., Haverschmidt 1968). Measurements for egg size range from 52 by 37 millimeters to 62.5 by 42.6 mm (Wetmore 1965). Two eggs from Suriname weighed 43 and 46 g (Haverschmidt 1968). Hatching is asynchronous and most often, only two chicks survive to fledging (Hancock et al. 1992). After two to three weeks, the parents only visit the nest to feed the young, which fledge at 23 to 27 days (Hancock et al. 1992). The young stay by the nest for a few days until they join the parents at feeding sites (Hancock et al. 1992).