The present paper is devoted to prediction of the performance of a combined system, consisting of a proton exchange membrane fuel cell integrated with an organic Rankine cycle (PEMFC-ORC). The PEMFC waste heat is recovered by an ORC system for electricity generation. The R123 was firstly selected as a working fluid which improved the net power and overall efficiency of the combined system by 13.76% and 5.19%, respectively, in comparison with the PEMFC system. Here, a validation study was conducted by comparing the obtained results with a literature based case. It was also outlined how stack operating pressures and temperatures affect the system performances. Moreover, an optimization study was performed to select the operating parameters values that maximize the system's power output. Accordingly, the net electrical output and overall efficiency of the system using the basic working fluid R123, have been improved by 16.17% and 5.47%, respectively.