Nitrogen is crucial for plant development and crop production. Amaranthus cruentus, a C₄ species, has been pointed out as a high-nutritious and stress resilient crop. Here we studied the effects of sufficient and low nitrogen supplementation on the photosynthetic efficiency and metabolic responses of A. cruentus. Photochemical parameters from dark-adapted and transient chlorophyll fluorescence measurements, antioxidant enzymes activity, and metabolomic analysis, were evaluated to depict the impact of nitrogen availability. Photochemical parameters showed a significant decrease compared to those from gas exchange. The antioxidant enzymes activity revealed variations among treatments, being important at low nitrogen availability. At the metabolic level, there is a significant accumulation of L-glutamine, aromatic amino acids and ascorbic acid in A. cruentus with sufficient nitrogen. At low nitrogen, the metabolic profile of A. cruentus suggests stabilization of membrane structure and efficient use of available nitrogen by accumulating L-glutamic acid. The differential accumulation of L-glutamine and L-glutamic acid reflects an adaptive strategy for maintaining nitrogen. Nitrogen-rich conditions, the plant stores excess nitrogen as L-glutamine, while in deficiency, it utilizes L-glutamic acid for essential metabolic functions. Overall, A. cruentus activates a coordinated metabolic strategy under LN to optimize nitrogen use. This includes effective ROS detoxification via both enzymatic and non-enzymatic antioxidants, structural reinforcement through membrane-stabilizing lipids, and efficient nitrogen storage and redistribution to meet metabolic demands during nitrogen limitation.