Nanotechnology represents an innovative approach to ameliorating abiotic stress in oilseed crops, with the application of iron oxide nanoparticles (FeO−NPs) gaining notable popularity recently. Therefore, we have utilized FeO−NPs as an alleviating agent on an oilseed crop, specifically rapeseed (Brassica napus L.), grown in soil with varying levels of arsenic (As). This study investigates various growth−related attributes, the efficiency of the photosynthetic machinery, indicators of oxidative stress, and responses of both enzymatic and non-enzymatic antioxidants, along with their specific gene expression, sugar content, organic acids exudation pattern and As accumulation in different parts of the plant. Our findings indicated that soil contaminated with As reduced crop growth, photosynthetic efficiency, and nutritional status in plants, while simultaneously enhancing oxidative stress indicators, organic acid exudation, activity of both enzymatic and non-enzymatic antioxidants and their related gene expressions, and endogenous As content in the shoots and roots of B. napus. Moreover, increasing levels of As in the soil caused a signifcant increase in proline and organic acids exudation pattern. However, the exogenous application of FeO−NPs enhanced plant growth and the photosynthetic rate in B. napus by boosting the antioxidant system and mineral status, and by reducing the concentrations of oxidative stress biomarkers, organic acids, and As accumulation in both roots and shoots. Hence, this study suggests that seed priming with FeO−NPs is an effective technique that can be employed to fortify nutrients and mitigate metal toxicity in areas polluted with metals.