Poleward extension of warm-affiliated species under climate change is drawing increased attention to the impacts of herbivores on temperate reefs. The generality of these impacts and vulnerability of temperate reef systems to overgrazing, however, remains unclear due to a low recognition of the environmental context within which changes are taking place. Here we review the taxonomic and functional diversity of herbivores and biogeographical differences in herbivore impacts on temperate reefs across Australia. We identified 100 studies that directly measured herbivory on temperate rocky reefs in Australia, representing a total of 1076 seaweed-herbivore interactions between 84 species of herbivore and 112 species of seaweed. In terms of function, herbivory fell into six main functional roles of which the 53 species from 5/6 classes of herbivore were recorded as grazers on turf and understorey seaweeds. Individual species also performed multiple functions on reefs highlighting the plasticity in species behaviour under different environmental contexts. Despite a relatively high diversity of herbivores, only two species have been documented to cause overgrazing of kelp forests at a reef-scape scale. Impacts of herbivory on temperate reefs are increasing in multiple regions, driven by increased densities of a small number of species that differ between regions. These changes mask broader underlying declines in herbivore diversity across temperate Australia in recent decades.