The development of bio-based materials is crucial for reducing the dependence on fossil resources. Being one of the major natural sources of aromatic scaffolds, lignin holds high potential for valorization, both for high-value added chemicals as well as its use as a macromonomer for lignin-based polymer production. This work presents an innovative approach to synthesizing fully bio-based non-isocyanate polyurethanes (NIPUs) thermosets partially based on lignin. In particular, lignin was modified to install cyclic carbonate moieties and to act as substitute for toxic and hazardous isocyanates commercially used for polyurethane (PU) production. NIPUs have attracted growing interest due to to their potential to replace conventional PUs, thus increasing the overall sustainability of the process without compromising the material properties.In this regard, the synthesis of a bio-based polyamine derived from high oleic sunflower oil using an efficient thiol–ene reaction, implemented in both batch and continuous flow processes, was optimized, demonstrating its scalability and milder conditions by using greener solvents. The obtained polyamine was employed as crosslinker with cyclic carbonate-functionalized lignin and a sugar-based third component, yielding fully bio-based non-isocyanate polyurethane (NIPU) thermosets. Comprehensive characterization of the resulting materials revealed a successful curing, promising thermal and surface properties, demonstrating their viability as potential greener alternatives to conventional polyurethanes. The successful integration of fully bio-based components not only advances the development of more sustainable polymers, but also contributes to reducing dependence on fossil fuel-derived materials. These findings highlight the potential of lignin in the transition toward environmentally friendlier, high-performance thermosetting polymers.