Industrial effluents contain a wide range of organic pollutants that present harmful effects on the environment and deprived communities with no access to clean water. As this organic matter is resistant to conventional treatments, Advanced Oxidation Processes (AOPs) have emerged as a suitable option to counteract these environmental challenges. Engineered iron oxide nanoparticles have been widely tested in AOPs catalysis, but their full potential as magnetic induction self-heating catalysts has not been studied yet on real and highly contaminated industrial wastewaters. In this study we have designed a self-heating catalyst with a finely tuned structure of small cores (10 nm) aggregates to develop multicore particles (40 nm) with high magnetic moment and high colloidal stability. This nanocatalyst, that can be separated by magnetic harvesting, is able to increase reaction temperatures (up to 90 °C at 1 mg/mL suspension in 5 min) under the action of alternating magnetic fields. This efficient heating was tested in the degradation of a model compound (methyl orange) and real wastewaters, such as leachate from a solid landfill (LIX) and colored wastewater from a textile industry (TIW). It was possible to increase reaction rates leading to a reduction of the chemical oxygen demand of 50 and 90%, for TIW and LIX. These high removal and degradation ability of the magnetic nanocatalyst was sustained with the formation of strong reactive oxygen species by a Fenton-like mechanism as proved by electron paramagnetic resonance. These findings represent an important advance for the industrial implementation of a scalable, non-toxic, self-heating catalysts that can certainly enhance AOP for wastewater treatment in a more sustainable and efficient way.