High-temperature stress poses a significant threat to agricultural productivity and ecological diversity. Here, we show the effects of prolonged high-temperature stress on wheat (Triticum aestivum) and the model grass Brachypodium distachyon and demonstrate that heat stress induces iron deficiency in newly emerged leaves. Quantitative trait locus analysis of B. distachyon reveals a genomic region associated with heat resilience that includes the transporter of mugineic acid family phytosiderophores 1 gene (BdTOM1). Iron-deficiency-related genes including BdTOM1 are more highly expressed in a high-temperature-tolerant B. distachyon accession at high temperature than in a sensitive accession, resulting in greater secretion of deoxymugineic acid. Treatment with proline-2′-deoxymugineic acid mitigates heat-induced growth inhibition, but excess iron treatment leads to toxicity in both species. Our findings highlight the role of heat-induced nutritional stress in prolonged high-temperature stress and suggest that iron homeostasis could provide a promising target for improving crop resilience to climate extremes.