Elif Kaynak, Igor Wachter, Vigneshwaran Shanmugam, Nurul Zuhairah Mahmud Zuhudi, Oisik Das
ABSTRACT Increasing concerns and regulatory restrictions associated with conventional flame retardants have driven research into halogen‐free and bio‐based alternatives that combine fire safety with reduced environmental impact. Lignin, a macromolecule prevalent in biomass, has emerged as a promising candidate for flame‐retardant applications owing to its intrinsic charring ability, high carbon content, and chemical versatility. This review provides a comprehensive and critical overview of lignin‐derived flame retardants, addressing fire behavior assessment, structure–property relationships, flame‐retardant mechanisms, and practical applications in polymers, coatings, textiles, and construction materials. The influence of plant origin and extraction method on thermal decomposition, char formation, and combustion behavior is discussed in detail, with particular emphasis on condensed‐phase mechanisms governing fire performance. Strategies employing unmodified lignin, chemically modified lignin (phosphorus‐, nitrogen‐, and silicon‐containing systems), lignin‐containing intumescent formulations, and lignin‐derived nanocomposites are systematically reviewed. Their effects on flammability metrics, heat release characteristics, smoke suppression, and mechanical performance are critically assessed. While lignin‐based systems demonstrate significant potential to reduce heat release and enhance char stability, challenges remain related to dispersion, compatibility, processing stability, and the sustainability of modification routes.