Thermal performance curves are useful for predicting how organisms might respond to environmental change, and are becoming increasingly applicable for ectothermic animals threatened by climate change. Here we present a thermal performance curve for the critically endangered western swamp turtle (Pseudemydura umbrina) based upon measurements of O₂ consumption and CO₂ production obtained by flow-through respirometry at temperatures between 15 and 30°C. Standard metabolic rate was significantly higher at 30°C (0.030 mL g^–1 h^–1 O₂, 0.021 mL g^–1 h^–1 CO₂) than at 20°C (0.007 mL g^–1 h^–1 O₂, 0.006 mL g^–1 h^–1 CO₂) and the 20−30°C Q₁₀ for O₂ and CO₂ were 4.60 and 3.55 respectively. Oxygen consumption rates at 15°C and 25°C were 0.002 (±0.000) and 0.018 (±0.000) mL g^–1 h^–1, with a corresponding Q₁₀ of 9.21. Beyond ∼30°C there was a decline in physiological performance, which was supported by activity patterns reported for P. umbrina in the literature.