The textile industry is among the major water-consuming industries, generating considerable volumes of wastewater with high organic pollution loads during washing, dyeing, and finishing processes. The presence of dissolved organic compounds, dyes, and processing additives increases the chemical oxygen demand (COD) of these effluents, and their direct discharge into the environment can lead to serious environmental consequences. Therefore, the application of effective and cost-efficient methods for reducing the organic pollution load of textile wastewater is essential. This study aimed to investigate the performance of a Moving Bed Biofilm Reactor (MBBR) in COD removal from textile wastewater and to evaluate the effect of Granular Activated Carbon (GAC) on improving the efficiency of this process. For this purpose, an MBBR reactor made of plexiglass with an effective volume of 30 L was designed and operated. The reactor was fed with simulated textile wastewater having an influent COD concentration of 2000 mg/L, and its performance was evaluated at a hydraulic retention time (HRT) of 24 hours. The results showed that the MBBR system had a high capacity for organic matter removal, with COD removal efficiency ranging from 86% to 92% under different operating conditions. In addition, the use of granular activated carbon in the hybrid MBBR GAC system enhanced the treatment efficiency. It improved effluent quality, increasing COD removal efficiency to more than 95%. The findings of this study indicate that MBBR and MBBR–GAC processes can be considered effective, stable, and cost-efficient approaches for the treatment of textile wastewater and the reduction of organic pollution load.