Rising night temperature negatively impacts food systems, human health, and ecosystem functions. A 1 °C increase in night temperature reduces yield of major cereal crops by 3–10%. However, the mechanisms of high night temperature (HNT) induced yield losses remain poorly understood. Using a series of controlled environment experiments, we investigated the impact of, and mechanisms underpinning, night warming in vegetative and reproductive traits of Australian wheat cultivars released between 1901 and 2012. These included photosynthetic capacity traits, specifically the maximum rate of Rubisco carboxylation (Vcmax25), the rate of electron transport (J25) and the rate of trios phosphate utilisation (TPU25), all measured at a common temperature of 25 °C, dark respiration (during the day, [Rday], and at night [Rnight]), and reproductive processes (pollen germination, pollen tube growth and spikelet fertility). Gas- exchange analyses conducted at a common day temperature (25 °C) showed that although net carbon assimilation (Anet) has increased over time under warm nights, Vmax and J25 have been declined markedly. Rnight has acclimated strongly to HNT, especially in older cultivars, suggesting historical genotypes may possess greater respiratory plasticity. Furthermore, HNT significantly increased CO2-based respiratory parameters including Q10 (proportional change in respiration per 10 °C change in temperature), and activation energy (Eo) and Rnight at reference rate (RREF) declined indicating a downregulation of basal respiratory capacity. In contrast, O2-based measures showed less pronounced (i.e. a more buffered response) except for significant decline in the maximum respiratory capacity (CapR) pointing to possible engagement of the alternative oxidase pathway. Strong correlations between apparent activation energy (EoREF) and the curvature of Rnight to warm nights (δ) highlighted the coordination between respiratory capacity and thermal sensitivity. These findings suggest that Rnight acclimation is dynamic and gas-specific, involving adjustments in mitochondrial pathway activity and thermal response regulation. Beyond its leaf metabolic effects, HNT also impaired reproductive development. In vivo assays revealed reduced pollen adhesion, germination, and tube elongation, contributing to lower spikelet fertility, grain weight, and tiller number. These reproductive disruptions varied among genotypes and were compounded by accelerated developmental transitions, that shortened the duration of spikelet formation and grain filling. Overall, the research identifies key physiological constraints imposed by HNT on wheat, revealing both acclimatory capacity and vulnerability. These insights underscore the need to integrate thermal tolerance traits into breeding programs and offer new directions for developing climate-resilient wheat cultivars under rising night-time temperatures.