Invasive fishes continue to adversely impact the structure and function of aquatic ecosystems globally. The effects of introduced populations may, however, differ according to key characteristics such as size, abundance, invaded habitat type, and community composition. Here, we conduct diet analyses to describe the feeding characteristics of the nonnative North American Pumpkinseed, Lepomis gibbosus, across multiple habitat types (three lentic and three lotic systems) and fish size classes. Pumpkinseeds exhibited a broad diet, inclusive of numerous threatened species groups (e.g., amphibians) and commonly included dipterans and detritus overall. Observed diets were more diverse in ponds compared to stream habitats, as well as for larger individuals, with individuals in streams tending to consume terrestrial insects in higher numbers. Our results show that the impact of Lepomis gibbosus differs not only according to size and ontogeny, but also depending on the habitat type, probably due to different prey availabilities and biotic interactions. This has implications for ecological impacts of this invasive species in lentic and lotic systems, with a generalist diet potentially facilitating impacts on a broad range of prey taxa, with concomitant adverse competitive effects on native predator species.