AbstractIron oxide and its carbon‐containing biochar have shown efficiencies in Fenton oxidation reactions in recent years. Though magnetic biochar composites have been reported, developing facile, environment‐friendly methods with appropriate activity remains challenging. Removing dye traces from aqueous solutions is a prime concern under water scarcity issues at different levels. We developed a catalyst of biochar with magnetite for dye remediation. Magnetite is homogeneously loaded on biochar surfaces to form Fe3O4‐biochar to efficiently activate H2O2 to achieve hydroxyl radicals. This catalyst degrades Fast green dye efficiently around 89.3 % within 60 min with the optimum reaction conditions of 15 mM Fast Green dye, pH=4, 30 mg of Fe3O4‐biochar and 25 mM of H2O2. The composite shows around 41 % increase in the degradation rate after incorporating the Fe3O4 on biochar. The prepared Fe3O4‐biochar composite can be easily recycled without significant activity loss for five successive degradation reactions. The reported study provided a direction to prepare newer Fenton catalysts from sustainable sources for the degradation of organic dyes in water and overcame individual limitations of Fe3O4 and biochar.