The integration of hierarchical nanostructure design and encapsulation strategies using a combination of chemical bath deposition, hydrothermal, and in situ reaction methods has been recognized as one of the most effective strategies to realize practical applications of various quantum-dot sensitized solar cell materials. Herein, a facile and scalable method is developed to synthesize a composite CoS–NiS counter electrode through low-cost chemical bath deposition followed by hydrothermal process. The proposed synthesis offers several advantages, including simplicity, efficiency, and low cost. The QDSSCs based CoS–NiS counter electrode under one-sun illumination (AM 1.5, 100 mW cm⁻²) yielded a high short circuit current density (J_sc) of 14.76 mA cm⁻², open circuit voltage (V_oc) of 0.590 V, fill factor (FF) of 0.450, and power conversion efficiency (η) of 4.70%. These values are much higher than those of the CoS and Pt CEs (η = 3.29% and 1.12%). The amount of NiS used in the synthesis process has a remarkable effect on the features of CoS nanospheres. Our studies have revealed that both the exceptional electrical conductivity of the NiS and the excellent catalytic activity of the CoS nanospheres improve the conversion efficiency of the uniformly CoS–NiS composite counter electrode. In the present study CoS–NiS composite has obtained higher electro-catalytic activity in comparison with CoS, and Pt CEs, which plays a crucial role to improve the high performance of QDSSC. The electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and Tafel-polarization measurements were used to investigate the electrocatalytic activity of the CoS–NiS composite, CoS and Pt CEs.