The Pythonidae are a widely distributed group of snakes that fill a variety of niches in Africa, Asia and Australasia. We used mark–recapture techniques to describe the life-history traits and colour change in the green python Morelia viridis, a species that is popular in the captive pet industry but poorly known in the wild. Modelling of growth rates revealed that males and females reach sexual maturity after 2.4 and 3.6 years, respectively, and are predicted to live for at least 15 years. Extrapolation from small individuals revealed a highly seasonal breeding period with hatching in late November. However, few hatchlings were recorded in any one year, suggesting that adults do not breed every year. The adult sex ratio did not differ from parity, but immature females outnumbered immature males. Approximately 50% of all snakes captured were adult sized. Sexual dimorphism was not detected in the adults, but juvenile females have larger heads than males. Ontogenetic colour change (OCC) from yellow to green occurred between 53 and 59 cm and, based on growth rates, occurs at c. 1 year of age. This change took place rapidly without an associated shedding of skin. Green pythons have a slow life history, and populations may be vulnerable to removal of individuals for the captive pet trade. They also provide excellent opportunities for examining the evolutionary significance of OCC.