Ocean sunfish (Mola spp.) have largely been considered as obligate gelativores, but recent research has suggested that they undergo an unusual life history shift. In this study, analyses of bulk and amino acid nitrogen (δ15N) and carbon (δ13C) stable isotope ratios were employed to provide detailed insight into ontogenetic variation in sunfish trophic ecology and habitat use and to assess whether any observed patterns were common to populations around the world. Through this combined approach, a clear ontogenetic shift was identified in both trophic ecology and habitat use of ocean sunfish, indicating a complex trophic role that changes from more benthic to pelagic prey on a continuous scale as fish grow larger. The data also revealed strong population structuring with potential to assess connectivity between distinct groupings using isotopic analysis. When combined, these new insights into sunfish ecology may be of value to conservation management teams, indicating a broad ecological role, distinct population clustering and possible trans-Atlantic movements. These results suggest that the current mass bycatch of ocean sunfish may have far-reaching ecological implications and further highlights the growing need for conservation management of this vulnerable genus.