Anthropogenic activities generate industrial wastewater, posing the greatest threat to the environment and requiring cleanup to mitigate environmental impacts and human health risks. Because of their remarkable characteristics, Fe₃O₄-based magnetic nanoparticles (MNPs) have recently gained popularity as powerful tools for wastewater treatment. To alleviate the qualitative strain on water supplies, MNPs have found newer applications owing to their inherent characteristics. Herein, the physical, chemical, and biological/green approaches for the synthesis and assembly of MNPs are deliberated, with biologically derived options found to be environmentally benign and sustainable in the long term. The efficacy of MNPs in the elimination or recovery of various wastewater contaminants, such as heavy metals, inorganic pollutants, dyes, biological pollutants, and microalgae, is presented. Moreover, the advantages and disadvantages of MNPs in their usage for wastewater treatment, the removal mechanism via coagulation, and the manufacture of MNPs are appraised in detail. Finally, the potential of Fe₃O₄-based MNPs for deployment in environmental cleanup and their future applications are addressed.