In this study, melting of a phase change material (PCM) in a square cavity with a single fin attached at the center of the heated wall is studied numerically employing the enthalpy-porosity method. The opposite wall to the heated wall in the square cavity is cold. The other two adjacent walls are thermally insulated. Paraffin wax is chosen as a PCM due to its demonstrable favorable properties. The thermophysical properties of the paraffin wax are assumed to be a dual function of temperature and phase. The influence of the fin length on the melting process of the paraffin wax is examined. Moreover, the orientation of the square cavity on the melting process is scrutinized. The numerical results elucidate that the melting rates increase significantly by embedding the fin into the paraffin wax. As the fin length is incremented, the melting rate intensifies considerably during the early stages of melting. However, the effect of the fin length on the melting rate diminishes after a long period of heating has happened. It is also observed that the melting rate can be augmented significantly by changing the orientation of the heated wall in the square cavity.