Abstract: With the rapid acceleration of global industrialization, soil contamination by heavy metals has become a critical environmental challenge, drawing significant attention from the scientific community. Chromium pollution is particularly pervasive, primarily stemming from industrial discharges such as leather processing, textile printing, and electroplating, as well as various agricultural activities. Cr predominantly exists in the trivalent Cr(III) and hexavalent Cr(VI) oxidation states. Although Cr(III) exhibits low mobility and is readily adsorbed onto soil particles, Cr(VI) is characterized by high solubility, mobility, and acute toxicity. Cr(VI) readily disperses through the vadose zone into the groundwater, posing a severe and persistent threat to ecological safety and human health. Electrokinetic (EK) remediation has emerged as a promising technology for treating low-permeability soils (such as clays) because of its unique electrically driven transport mechanism. However, given the complexity and heterogeneity of actual soil contamination, employing a single remediation technique often fails to achieve the desired pollutant removal efficiency. To overcome this technical bottleneck, an integrated electrokinetic–permeable reactive barrier (EK–PRB) system is designed and optimized in this study. The objective was to achieve in situ interception and removal of migrating pollutants by incorporating a chemically modified activated carbon PRB layer. The synergistic mechanisms between various electrolytes and PRB materials was systematically investigated to optimize the system performance. Specifically, activated carbon was functionalized using hydrochloric acid and cetyltrimethylammonium bromide (a cationic surfactant), to precisely regulate the pore structure and surface charge characteristics of the material. Three electrolytes with distinct driving mechanisms were introduced: citric acid (a complexing agent), potassium chloride (a conductive salt), and sodium dodecylbenzenesulfonate (an anionic surfactant). The remediation efficacy was comprehensively evaluated by monitoring key parameters, including electrical current evolution, soil pH distribution, and spatiotemporal migration patterns of Cr. The experimental results indicate that the remediation efficiency is heavily dependent on the physicochemical compatibility between the electrolyte and the PRB material. The combination of a citric acid (CA) electrolyte with hydrochloric acid-modified activated carbon demonstrated optimal performance, achieving removal rates of 93.10% for Cr(VI) and 77.96% for total Cr. Mechanistically, this superior performance was attributed to the strong chelating action of CA, which effectively prevented precipitation and promoted the desorption of adsorbed Cr from soil particles. Simultaneously, the acid-modified PRB layer provided abundant active sites and favorable surface conditions for the precise interception of migrating chromium-citrate complexes. Comparative analysis confirmed that the anolyte Cr concentration in the EK–PRB remediated group was significantly lower than that in the conventional EK remediated group, verifying the efficacy of the PRB layer in mitigating anode enrichment. Furthermore, BCR (Bureau Communautaire de Référence) sequential extraction analysis revealed that the designed technology substantially altered the chemical speciation of the residual Cr. Post-remediation, the soil exhibited reductions exceeding 91.2% and 64.12% in the bioavailable weak acid extractable and reducible fractions, respectively, which are considered the most environmentally hazardous forms. In summary, compared to conventional EK remediation, the proposed EK–PRB technology not only achieves high-efficiency remediation but also promotes uniform removal and deep stabilization of Cr, offering a robust solution for the remediation of Cr-contaminated sites.