<p>In the present study, we investigated the role of magnesium (Mg) and boron (B) supplementation for the mitigation of arsenite (As³⁺) stress in rice seedlings. As³⁺ stress reduced the seedling growth, biomass, and pigment content, besides inducing necrotic lesions in the shoot and the onset of seminal root senescence. As³⁺ stress imposition also resulted in the overproduction of reactive oxygen species (ROS) and elevated the levels of oxidative stress markers such as malondialdehyde (MDA) and carbonyl proteins. As³⁺ stress also reduced the activities of antioxidant enzymes such as catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), and superoxide dismutase (SOD), and also the levels of ascorbate (AsA) and reduced glutathione (GSH). The metabolomic analysis clearly revealed that As³⁺ stress caused a substantial variation in the metabolite pool of the rice seedlings, resulting in a major metabolic shift in response to the stress. The supplementation of Mg and B in excess strongly mitigated the effects of As³⁺ stress by improving the plant performance, which was evident from improved seedling growth, higher biomass, high pigment levels, and substantially lower symptoms of leaf necrosis and seminal root senescence, compared to those under As³⁺ stress alone. Mg and B supplementation during As³⁺ stress resulted in a significant reduction in ROS, MDA, and carbonyl protein levels along with enhanced antioxidant metabolism. Mg and B supplementation caused the accumulation of distinct metabolites, which may be crucial for stress amelioration. The study reflected Mg and B supplementation as an effective nutrient management strategy for As³⁺ stress mitigation.</p>