The most detailed information on the nesting of the Sungrebe is from the observations in southern Mexico by Alvarez del Toro (1971), who discovered a nearly completed nest on 15 April. In Costa Rica, the Sungrebe breeds during the "early wet season" (Stiles and Skutch 1989); in Costa Rica the wet season typical begins in mid April. Two nests with eggs were reported from Panama in June and July (Wetmore 1965).
Both sexes contribute to nest construction (Alvarez del Toro 1971). The nest is a platform of twigs and reeds; a nest in Mexico was lined with dead leaves (Alvarez del Toro 1971). This nest was 22 cm across and 7 cm deep. Dimensions of a nest in Panama were 18.0 cm x 22.5 cm (Wetmore 1965). The nest is placed in vegetation directly overhanging the water, about a meter above the water's surface (Wetmore 1965, Alvarez del Toro 1971). The clutch size is two to four eggs (Wetmore 1965, Alvarez del Toro 1971). The eggs are buffy white, and are "spotted finely with cinnamon and pale purple rather uniformly over the entire surface" (Wetmore 1965). Dimensions of the eggs are 26.1-27.3 mm x 20.1-20.9 mm (n=3; Wetmore 1965) and 29-30 mm x 20 mm (n=2; Alvarez del Toro 1971).
Both sexes share incubation duties: the male incubates the eggs during the middle of the day, while the female sits on the nest for the remaining daylight hours and overnight. The Sungrebe has the surprisingly short incubation period of only 10-11 days. Unlike the African and Masked Finfoot, which have precocial chicks, Sungrebe chicks are highly altricial; they are almost naked, with only sparse down and short, poorly-formed bill and feet (Alvarez del Toro 1971).
After hatching, the male parent is more active in caring for the young, sheltering them in a shallow pocket under his wing, which is formed by a pleat of skin. The pocket is made more secure by the feathers on the side of the body. The young are carried this way even during swimming and flying. As the chicks advance, they can start to ride on their father's back, even during dives. The young are not nidifugous. It is not known how the chicks are placed in the pocket and how (and if) the male feeds the chicks there (Alvarez del Toro 1971).