This study evaluates the efficiency and adsorption mechanism of Remazol Black dye removal from textile wastewater using quaternary ammonium polymers (QAPs) as adsorbents. The adsorption behavior was systematically investigated through isotherm, kinetic, and thermodynamic analyses to elucidate the interaction mechanisms between the dye molecules and the adsorbent. Batch adsorption experiments were conducted to examine the effects of adsorbent dosage, contact time, temperature, and initial dye concentration. Adsorption data were analyzed using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models, while kinetic behavior was evaluated using pseudo first order and pseudo-second-order models. Surface and structural characterizations before and after adsorption were performed using SEM, FTIR, and BET analyses to identify morphological changes and functional group interactions. The optimum adsorption conditions were achieved at an adsorbent dosage of 0.10 g, a temperature range of 25–30 °C, and a contact time of 20–30 minutes, resulting in removal efficiencies of 97.65% for synthetic dye solutions and 95.64% for textile wastewater. The Langmuir model provided the best fit, indicating monolayer adsorption, while the pseudo-second-order kinetic model suggested chemisorption as the dominant rate-controlling mechanism. Thermodynamic parameters (ΔH° = 65.37 kJ/mol, ΔS° = 0.21 kJ/mol·K, and ΔG° values ranging from +1.54 to –8.10 kJ/mol) indicated that the adsorption process is endothermic and becomes spontaneous at elevated temperatures. A decrease in removal efficiency in textile wastewater compared to synthetic solutions was attributed to matrix effects, including the presence of competing ions and organic substances. The findings provide mechanistic insights into the adsorption performance of QAPs for dye removal from complex aqueous systems