High temperature has been a major limiting factor for wheat (Triticum aestivum L.) productivity and will become a significant driver of yield loss as global warming progresses. Many wheat-growing regions worldwide experience terminal heat stress during the grain-filling period, resulting in grain yield reduction. A sustainable solution to mitigate heat stress-induced damage is to develop heat-tolerant cultivars. To achieve this, identifying tolerant lines is essential to incorporate heat stress resilience into commercial varieties. Our working hypothesis was that retaining chlorophyll content during post-flowering heat stress will reduce yield losses. In this study, we evaluated the terminal heat stress tolerance of 254 diverse spring wheat lines from North American and Australian wheat-breeding programs in two independent experiments. The plants were grown in individual pots under controlled environments. Significant genetic variation was observed for the ability to retain post-stress chlorophyll content and yield components. Grain yield per plant and individual grain weight were significantly correlated with chlorophyll content under heat stress. The reduction in grain yield per plant was contributed more by the reduction of the individual grain weight than by the grain number under heat stress. A highly tolerant line, cultivar Otis, retained 79.2% chlorophyll content relative to control, and also recorded 55% greater chlorophyll content than the average of all 254 lines, at the end of 16 d of severe heat stress treatment. Mapping populations are being developed using Otis, with an aim to identify the genetic basis of chlorophyll retention under terminal heat stress. Resilient wheat lines identified with high grain weight under stress will serve as useful resources for abiotic stress breeding programs.