Body sizes and morphological traits of animals are often strongly influenced by their diet. Several studies have shown this to be true for snakes and have linked intraspecific differences in these attributes to geographic and sexual variations in prey sizes and diet. To help clarify anecdotal reports of morphological variation among populations of Green Pythons (Morelia viridis), we assessed geographic and sexual variations in the body size, morphology, and diet of 908 individuals from five sites in Australia and New Guinea. Body sizes and morphology differed among populations and, although some variation could be explained by sampling biases, we found no significant geographic dietary variation to help explain these differences. Juvenile Green Pythons preyed exclusively on small lizards and adults preyed on mammals, while birds comprised only 2.5% of all dietary records. Within all populations females grow to larger body sizes, although we observed little sexual dimorphism in other traits. Males and females selected the same prey types. However, large females, despite their larger overall size, consumed a greater proportion of small, diurnal prey (lizards and birds) than did males, suggesting a niche divergence. Although the two New Guinean mainland populations of Green Python are the most genetically divergent from one another, they are the most morphologically similar. Our data provide weak evidence to reject nonadaptive processes as creating geographic variations in the body sizes and morphology of Green Pythons and suggest that a better understanding of the relative importance of different prey may elucidate the mechanisms involved.