Abstract In this study, two-phase flow in a Polymer Electrolyte Membrane (PEM) fuel cell with the converging-diverging flow field was investigated using numerical simulation. A transient, three-dimensional, two-phase flow, and multi-component model, as well as an agglomerate model for oxygen reduction in the cathode catalyst layer, was employed to simulate the performance of the cathode half-cell. The numerical implementation was conducted by developing a new solver in OpenFOAM by the author. An augmentation about 28.2% was observed in the oxygen mass fraction at GDL/Channel interface for a PEM fuel cell with a converging-diverging angle of 0.3° in comparison with the reference cell (straight channels). Moreover, the average of liquid water saturation was decreased by 3.61% in the middle cross-section of gas channels and 9.4% near to the outlet region for reviewed converging-diverging cases. Finally, to investigate the improvement of the cell performance, polarization curve and net output power were presented. It was found that the using converging-diverging flow field was more effective at high current densities, while it had a minor effect at low current densities. The net output power of the PEM fuel cell with converging-diverging channels was enhanced by more than 10% compared with the base cell.