Paper sludge can be directly pyrolyzed into activated carbon, but its adsorption capacity remains limited. This study presents a simple ethylenediamine dihydrochloride-assisted activation method to transform paper sludge into nitrogen-doped porous carbon adsorbents for efficient hexavalent chromium (Cr(VI)) removal. Characterization results confirm that ethylenediamine dihydrochloride effectively introduces nitrogen dopants and significantly increases the specific surface area. The best-performing nitrogen-doped porous carbon exhibits a large specific surface area (1244 m2/g) and a high Cr(VI) adsorption capacity (193.6 mg/g). Adsorption experiments reveal a spontaneous, endothermic chemisorption process following pseudo-second-order kinetics and a Langmuir model. X-ray photoelectron spectroscopy (XPS) analysis further indicates that Cr(VI) is reduced and adsorbed onto nitrogen-containing functional groups in the porous carbon. This work demonstrates a chemical activation approach for converting paper sludge into high-performance porous carbon adsorbents, offering a valuable solution for hazardous metal removal and paper sludge valorization.