Environmental contamination by cadmium (Cd), a highly toxic heavy metal, poses significant health risks to plants and humans. Biochar has been effectively used to promote plant growth and productivity under Cd stress. This study presents an innovative application of biochar derived from the invasive weed Parthenium hysterophorus to promote plant growth and productivity under Cd stress. Our research includes detailed soil and plant analyses, providing a holistic perspective on how biochar and urea amendments influence soil properties, nutrient availability, and plant physiological responses. To address this, we established seven treatments: the control, Cd alone (5mgkg−1), biochar alone (5%), urea alone (3gkg−1), biochar with Cd, urea with Cd, and combination biochar and urea with Cd. Cd stress alone significantly reduced plant growth indicators such as shoot and root length, fresh and dry biomass, chlorophyll content, and grain yield. However, supplementation with biochar, urea, or their combination significantly increased shoot length, by 48%, 34%, and 65%, respectively; root length by 73%, 46%, and 70%; and fresh shoot biomass by 4%, 31%, and 4%, respectively, by enhancing soil physicochemical properties and increasing nutrients absorption. The biochar–urea combination also enhanced Cd tolerance by improving total chlorophyll content by 14%, 13%, and 16% relative to the control, and significantly (p <0.05) boosted the activity of antioxidant enzymes such as catalase, peroxidase, and superoxide dismutase by 51%, 30%, and 51%, respectively, thereby mitigating oxidative stress as a defensive mechanism. Cd tolerance was improved by biochar, urea, and their combination, which reduced Cd content in the shoots (by 60.5%, 38.9%, and 51.3%, respectively), roots (by 47.5%, 23.9%, and 57.6%, respectively), and grains (by 58.1%, 30.2%, and 38.3%, respectively) relative to Cd stress alone. The synergistic effects of biochar and urea is achieved through improved soil properties, nutrient availability, activating antioxidant defense mechanisms and minimizing accumulation of metal ions in plant tissues, thereby bolstering plant defenses against Cd stress. By converting invasive Parthenium weed into biochar and combining it with urea offers an environmentally friendly solution to manage its spread while effectively mitigating Cd stress in crops.