Nitrate (NO3ˉ) toxicity is a serious problem that threatens the health of living organisms and especially agricultural production. The presence of NO3ˉ leads to biomass loss by causing the imbalance of biochemical metabolism and inhibiting photosynthetic activity. A new critical approach to cope with nitrate toxicity is the use of polyamines (PAs) as an antioxidant defence system enhancer in plants. However, there is no information about the impacts of cadaverine, is one of PAs, on chloroplasts of plants exposed to NO3ˉ toxicity. For this purpose, this study focused on the photosynthetic and biochemical process taking place in chloroplasts of Triticum aestivum under nitrate stress (100 mM and 200 mM NO3ˉ) and/or cadaverine (100 µM and 1 mM Cad). Gas exchange, chlorophyll fluorescence (Fv/Fm and Fv/Fo), the efficiency of the light reaction (ΦPo/(1 − ΦPo)), the performance index (PItotal), and relative water content (RWC) levels were suppressed under NO3ˉ stress. Stress did not improve the antioxidant activities in chloroplasts such as superoxide dismutase (SOD), glutathione reductase (GR). After 100 mM NO3ˉ exposure, Cad increased chloroplastic SOD, peroxidase (POX), ascorbate peroxidase (APX), GR, monodehydroascorbate reductase (MDHAR), and glutathione S-transferase (GST) activities. In the presence of 200 mM NO3ˉ, Cads decreased SOD and GST activity. In NO3ˉ + Cad-applied wheat, the high contents of hydrogen peroxide (H2O2) and lipid peroxidation (TBARS) were effectively removed through ascorbate (AsA) regeneration. Cads promoted the maintenance of cellular redox state by regulating antioxidant pathways included in the ascorbate–glutathione (AsA-GSH) cycle. Our results showed that Cad has great potential to confer tolerance to wheat by reducing oxidative damage and protecting the biochemical reactions of photosynthesis against NO3ˉ toxicity.