Proton Exchange Membrane fuel cells (PEMFC) are recognized for their high efficiency and low environmental impact as energy conversion devices. The performance of PEMFCs, however, is highly sensitive to operating conditions such as temperature and voltage, affecting electrochemical reaction rates and overall thermal management. This study develops a 3D mathematical model using COMSOL Multiphysics software to evaluate the performance of a nonisothermal PEMFC under different operating voltage conditions (0.9 V, 0.7 V, and 0.5 V). Unlike previous studies that often assume isothermal conditions, this work explicitly accounts for heat transfer effects and their impact on fuel cell behavior. Key parameters analyzed include water activity in the gas phase and membrane, oxygen and water mole fraction, distribution of temperature, and electrolyte current density. It has been observed that at 0.5 V, there is a substantial reduction in O2 concentration, showing that the fuel cell is using a lot of O2, which enhances efficiency overall. The results offer insights into the impact of varying operating voltages on PEMFC performance and highlight the importance of thermal management and voltage regulation.