Across a breadth of animal taxa, early-life environmental variation has been demonstrated to have lasting effects on later-life traits, including brain morphology. Here, we use Plains Spadefoot Toads (Spea bombifrons) to evaluate how larval diet type and amount influence later-stage, juvenile brain size and the relative sizes of brain regions. We specifically investigate whether developmental plasticity in brain morphology mirrors previously documented interspecific variation with relation to nutritional restriction and carnivory. Our findings demonstrate, contrary to expectation, that exposure to dietary restriction during the larval stage causes an increase in relative juvenile brain size. However, consistent with our predictions, consuming a prey-based shrimp diet during the larval stage results in relatively larger juvenile telencephalons, an intraspecific response that parallels an interspecific pattern in frogs where more-carnivorous species possess relatively larger telencephalons. Our results demonstrate that early-life dietary restriction and early-life diet type can generate changes in juvenile brain size and morphology in ways that may influence later-life behaviors and fitness. Further, our study suggests that intraspecific and environmentally induced changes in brain morphology can mirror interspecific divergence in brain morphology, supporting a role for developmental plasticity in promoting evolutionary change.