The combined use of stable carbon and oxygen isotopes in plant matter is a tool of growing interest in cereal crop management and breeding, owing to its relevance for assessing the photosynthetic and transpirative performance under different growing conditions including water and N regimes. However, this method has not been applied to wheat grown under real field conditions. Here, plant growth, grain yield (GY) and the associated agronomic components, carbon isotope discrimination (Δ13C) plus oxygen isotope composition (δ18O) as well as leaf and canopy gas exchange were measured in field-grown wheat subjected to different water and N availabilities. Water limitation was the main factor affecting yield, leaf and canopy gas exchange and Δ13C and δ18O, whereas N had a smaller effect on such traits. The combination of Δ13C and δ18O gave a clear advantage compared with gas exchange measurements, as it provides information on the instantaneous and the long-term plant photosynthetic and transpirative performance and are less labour intensive than gas exchange measurements. In addition, the combination of plant Δ13C and δ18O predicted differences in GY and related agronomical parameters, providing agronomists and breeders with integrative traits for selecting crop management practices and/or genotypes with better performance under water-limiting and N-limiting conditions.