Current population irruptions of crown-of-thorns starfish (Acanthaster cf. solaris; CoTS) and emerging effects of global climate change are contributing to the ongoing degradation of the Great Barrier Reef (GBR). Yet, little is known about how coral-feeding CoTS may fare in a warmer ocean. We measured various physiological and behavioural responses, as well as the survival of CoTS exposed to different thermal environments reflecting current temperatures experienced on the GBR, and those projected under near-future climate change. We found that metabolic and activity rates of CoTS increased from 26 to 30 °C, but declined at 32 °C. At this temperature, survival of CoTS was also significantly reduced. These findings indicate that 32 °C is above the thermal optimum of CoTS, suggesting that near-future ocean warming may undermine the performance and survival of this species. Still, any ecosystem benefits arising from detrimental effects of ocean warming on CoTS, are likely to be offset by direct effects of elevated temperatures on corals.