Several industrial and agricultural practices contribute significantly to water contamination. These activities release several amount of pollutants, including pesticides, heavy metals, and organic compounds, into water sources, posing health risks and causing environmental damage. Industries such as mining, textiles, and pharmaceuticals discharge harmful toxins, further polluting water. Processes like ball-milling, adsorption, filtration, and flocculation are commonly used for wastewater treatment. Recent advancements have focused on the study of green nanomaterials (NMs), particularly cellulose-based and lignin-based NMs, due to their various properties, biodegradability, and low toxicity. This review covers the fabrication methods, modification techniques, and applications of cellulose-based and lignin-based NMs, such as cellulose nanofibers, nanocrystals, lignin-based aerogels, and hydrogels for wastewater treatment. The unique properties of lignin and cellulose, including their high surface area, functionalization, and biocompatibility, make them suitable for water purification. The paper also discusses a SWOT analysis, which will be useful for future researchers, highlighting both opportunities and challenges in this area. This paper aims to provide valuable insights into ongoing research and development in cellulose and lignin-based nanomaterials for next-generation water treatment solutions.