Lignin holds great promise for fabricating multifunctional carbon materials, yet it is hindered by the difficulty of simultaneous pore structure regulation and heteroatom doping. To address this challenge, we propose a novel molten KCl-thiourea synergistic strategy for the scalable synthesis of N/S co-doped lignin-derived porous carbons without additional chemical activators. Molten KCl provides a growing environment to inhibit carbon agglomeration, guiding the formation of a hierarchical micropore-mesopore structure. Thiourea serves as a multi-role precursor: it crosslinks lignin-derived fragments to prevent structural collapse, acts as an in-situ N/S source, and reacts with residual Na+in lignin to form water-soluble salts for in-situ desalination. The optimal sample exhibits a high surface area of 1802 m2⋅g 1, a balanced pore size distribution, and a heteroatom content of N/S for CO2 adsorption (5.7 mmol⋅g 1) and supercapacitor applications (345F⋅g 1 at 0.1 A⋅g 1 and 98% capacitance retention after 10,000 cycles). This work not only provides a sustainable and cost-effective route for lignin valorization but also reveals the synergistic mechanism of molten salts and heteroatom precursors in regulating carbon structures. The resulting carbons exhibit great potential for practical applications in carbon capture and electrochemical energy storage.