Potassium-ion batteries (PIBs), with a bigger shuttling cation (K+), compete with Lithium-ion batteries (LIBs) for future energy storage due to the higher mobility of the solvated ions and lesser desolvation energy during energy storage. Developing stable anode material with excellent battery metrics is challenging in PIBs. Graphite, a promising anode for PIBs, faces poor structural stability from massive volume expansion of 61% during intercalation. The hard carbons (HCs) with a pseudo graphitic domain with rich pores and defects can accommodate more potassium ions without significant structural degradation. In this work, we upcycled the polyvinylidene chloride (PVC) to synthesize low-cost, green, and sustainable HCs anode material for PIBs. PVC-derived HCs from commercial and waste PVC shows high reversible capacities of 477 mAh g−1 and 378 mAh g−1, respectively, at 0.1C, much superior to the reported HCs. The pore morphology is critical for the battery performance, with the partially closed ink-bottle-shaped mesopores of CPVC exhibiting better initial Coulombic efficiency (ICE) than the wedge-shaped open pores of WPVC. The distinct K+ storage mechanism is revealed through differential capacity plots, GITT, and CV analysis to confirm a three-stage storage via surface adsorption, intercalation, and pore-filling mechanism. The full-cell KǁPBA, using Prussian white as the cathode, delivers 284 Wh kg−1 with 93% retention over 1000 cycles at a 1C rate. Upcycling PVC plastics into value-added HC battery electrodes with excellent performance helps generate cost-effective and sustainable resources for a circular materials economy and provides a cheap, green, and sustainable anode material for PIBs.