Abstract: Polyvinyl chloride (PVC) is one of the most widely produced general-purpose plastics globally, owing to its outstanding mechanical properties, excellent corrosion resistance, and versatile processability. These attributes make PVC indispensable in construction materials, municipal pipelines, medical devices, and various other applications. Nevertheless, the chlorine content in PVC molecular structures accounts for up to 57.00 wt%, posing severe environmental and operational challenges, including a high risk of corrosive gas release, equipment deterioration, and extremely low recyclability of chlorinated waste streams. To address these challenges, this study develops a tandem process integrating oxidative hydrothermal treatment (HT) with Joule heating pyrolysis to achieve both harmless disposal and resource recovery of PVC wastes. In the first stage, subcritical water containing hydrogen peroxide (H₂O₂) was employed to promote efficient and environmentally benign chlorine removal, safely transferring chlorine species into the aqueous phase. The resulting dechlorinated carbonaceous residue was subsequently used as the feedstock for Joule heating catalytic pyrolysis, enabling the concurrent production of high-purity graphene and hydrogen gas. Experimental results demonstrated that the oxidative hydrothermal system significantly enhanced deep dechlorination. Under identical conditions (250 °C, 3 h), the non-oxidative hydrothermal route achieved a dechlorination efficiency of only 12.69%, whereas the oxidative system with 3 wt% H₂O₂ reached a remarkable efficiency of 99.22%, effectively overcoming the energy barriers limiting conventional thermal treatments. Notably, this oxidative HT system also inhibited excessive mineralization of the carbon framework, retaining 78.00–81.10% of the original carbon in the solid-phase product, which formed a porous carbonaceous architecture favorable for subsequent conversion. Material characterizations, including FTIR, ¹³C NMR, and XPS, revealed that dehydrochlorination was the primary pathway for PVC hydrothermal depolymerization, driving the transformation of the chlorine-bearing saturated main chain into unsaturated polyene structures. Meanwhile, oxidation promoted the formation of oxygen-containing functional groups, while the generated unsaturated bonds further facilitated the cyclization and aromatization of low-molecular-weight olefins. The liquid-phase products were predominantly aromatic oxygenates, such as benzaldehyde and acetophenone, supporting the proposed reaction network. In the second stage, the dechlorinated carbonaceous skeleton was efficiently converted into high-value graphene through rapid Joule heating treatment, taking advantage of the preformed porous structure and abundant defect sites. A comprehensive techno-economic analysis (TEA), based on the graphene recovery pathway, confirmed that this integrated strategy generated a net profit exceeding RMB 20,000 per ton of processed PVC waste, demonstrating strong economic potential for industrial-scale implementation. Collectively, this work establishes a clean, cost-effective, and promising pathway for upcycling chlorine-laden plastics, converting hazardous waste management challenges into opportunities for functional material synthesis and energy recovery.