This study synthesized a novel biochar through the slow pyrolysis of moringa seed cake, a de-oiled cake obtained as a by-product of oil extraction, and analyzed its physicochemical properties. The results revealed that the biochar exhibits a high pH and abundant surface functional groups, making it a promising material for lead adsorption. The research further investigated the impact of biochar content (0% to 10% w/w) and curing time on stabilizing soil contaminated with lead at concentrations of 5,000 mg/kg and 10,000 mg/kg. The toxicity characteristic leaching test (TCLP) demonstrated that treatment with 10% w/w biochar combined with 28 days of curing reduced lead leachability to within regulatory limits, achieving over 89% immobilization efficiency. Additionally, soil strength and pH progressively increased with higher biochar content and longer curing durations, maintaining stability after 56 to 90 days. Microstructural analysis revealed the mechanisms responsible for effective lead stabilization, including lead precipitation, surface complexation with functional groups (C═O, O═C─O), and encapsulation in calcium silicate hydrates (C─S─H).