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SUMMARY: High temperature stress inhibits photosynthesis and threatens wheat production. One measure of photosynthetic heat tolerance is Tcrit – the critical temperature at which incipient damage to photosystem II (PSII) occurs. This trait could be improved in wheat by exploiting genetic variation and genotype‐by‐environment interactions (GEI). Flag leaf Tcrit of 54 wheat genotypes was evaluated in 12 thermal environments over 3 years in Australia, and analysed using linear mixed models to assess GEI effects. Nine of the 12 environments had significant genetic effects and highly variable broad‐sense heritability (H2 ranged from 0.15 to 0.75). Tcrit GEI was variable, with 55.6% of the genetic variance across environments accounted for by the factor analytic model. Mean daily growth temperature in the month preceding anthesis was the most influential environmental driver of Tcrit GEI, suggesting biochemical, physiological and structural adjustments to temperature requiring different durations to manifest. These changes help protect or repair PSII upon exposure to heat stress, and may improve carbon assimilation under high temperature. To support breeding efforts to improve wheat performance under high temperature, we identified genotypes superior to commercial cultivars commonly grown by farmers, and demonstrated potential for developing genotypes with greater photosynthetic heat tolerance. Significance Statement: Here we examined intraspecific variation in photosynthetic heat tolerance (the critical temperature at which damage to PSII occurs ‐ Tcrit); effects of genotype‐by‐environment interactions on Tcrit; and environmental drivers of Tcrit in wheat – the most widely cultivated crop. Our study provides a sound framework for identifying germplasm with superior Tcrit relative to well‐adapted commercial cultivars. This framework can be applied in agricultural and ecological settings in selection of more heat tolerant species. [ABSTRACT FROM AUTHOR]