Water eutrophication caused by excessive ammonium (NH₄⁺-N) and phosphate (PO₄³⁻) discharge from wastewater poses severe environmental and public health risks. This study investigates the adsorption performance of magnesium-activated biochar (Mg-biochar) synthesized from locally sourced waste materials—temple waste, coconut husks, and wood—for simultaneous ammonium and phosphate recovery from wastewater. The biochar was produced via pyrolysis at 500°C and subsequently activated with magnesium chloride (MgCl₂) to enhance adsorption efficiency. Batch experiments were conducted using synthetic wastewater containing ammonium and phosphate (50–300 mg/L), evaluating the effects of contact time, biochar dosage, and pH on adsorption performance. The results showed that Mg-biochar achieved a maximum ammonium adsorption capacity of 24.39 mg/g and a phosphate adsorption capacity of 5.57 mg/g, with ammonium removal reaching 80% within the first 30 minutes of contact. Adsorption kinetics followed a second-order model (R² = 0.9999 for ammonium and 0.986 for phosphate), indicating chemisorption as the dominant mechanism. Isotherm analysis revealed that adsorption was best described by the Freundlich model, suggesting heterogeneous adsorption behaviour. This study highlights the potential of Mg-biochar as a cost-effective, sustainable solution for nutrient recovery in wastewater treatment, aligning with circular economy principles by converting organic waste into high-value adsorbents. The findings contribute to the development of low-cost, scalable, and efficient biochar-based technologies for mitigating nutrient pollution and improving wastewater management.