The global proliferation of heavy metal and organic pollutant contamination presents a significant challenge to water and soil ecosystems, necessitating the development of effective and sustainable remediation technologies. Lignin, an abundant and often underutilized biopolymer from agricultural and nonwoody sources such as rice husks, sugarcane bagasse, and corn stover, has emerged as a promising bio-based adsorbent. Nonwoody lignin, in particular, exhibits distinct structural characteristics, including a higher abundance of reactive functional groups like phenolic hydroxyl and carboxyl groups, making it highly effective for pollutant removal. This chapter provides a comprehensive review of the potential of nonwoody lignin as a biosorbent. It explores the fundamental adsorption mechanisms, including chelation, ion exchange, and electrostatic interactions for heavy metals, as well as—stacking and hydrophobic interactions for organic pollutants. Furthermore, the chapter details various modification strategies, such as sulfonation, amination, and the creation of nanostructured composites, which are crucial for enhancing adsorption capacity and selectivity. We present an overview of its applications in removing a range of pollutants, from toxic heavy metals like and to challenging organic contaminants such as dyes, pharmaceuticals, and pesticides. The discussion also covers critical aspects of adsorbent regeneration and reusability, highlighting the cost-effective material, long-term application. Finally, we address the challenges, including the variability of lignin sources and scalability issues, that are integral to a circular economy and sustainable water treatment.