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Rubisco activase uses energy from ATP hydrolysis to remove inhibitory sugar-phosphates from the active sites of Rubisco. In doing so, Rubisco activase adjusts the rate of CO₂ fixation by Rubisco to the prevailing light environment. However, its ability to maintain Rubisco active declines at temperatures above the optimum for plant growth, limiting carbon assimilation and biomass production. We characterised the biochemical properties of the three wheat Rubisco activase isoforms and identified one isoform that is more thermotolerant and a separate isoform that is faster at activating Rubisco. The abundance of the thermotolerant isoform increased in plants exposed to heat stress, but still represented less than 10% of the total Rubisco activase in the leaf. A specific amino acid residue was identified that confers enhanced thermal tolerance without affecting the efficiency of Rubisco activation. These results can be exploited to improve the climate resilience of carbon assimilation of wheat as temperatures become warmer and more volatile.