The exceptional morphological diversity of reef-associated species is a long-appreciated feature of teleost fishes. However, the major factors that influence the body shape of reef fishes are poorly known. Feeding mode is a good candidate for affecting body shape, as it determines many aspects of a fish’s life. We explored the effect of feeding mode on body shape in 1,530 species of reef fishes. We used a dataset of 8 linear measurements capturing body depth, width, and length using specimens from the National Museum of Natural History. Species were categorized by how they capture their prey, including those that capture most of their prey with direct biting actions on the substrate; species that capture prey only with suction; and species that regularly use both methods. A fourth category, “ram biting”, included species for whom direct biting actions of the jaws play a major role in pelagic prey capture. We found that the major axis of body shape variation, which describes a spectrum ranging from eels to triggerfishes, aligns closely with a gradient associated with the method of prey capture. Attached prey biters and species that use both feeding modes have deeper, more laterally compressed body shapes. In contrast, ram biters typically have more elongate body shapes that are nearly absent among species that use any amount of attached prey biting. Furthermore, feeding mode affects diversity of body shapes, as suction feeders had nearly twice the disparity as the most exclusive biters or species that use both feeding modes. Our results demonstrate that transitions to any use of biting result in a deeper body shape, revealing that prey capture method is a major determinant of body shape in reef fishes.