This study investigates the combined effect of a ship's leeway angle and regular waves on the added wave resistance of a general cargo vessel, which is a key factor in energy efficiency. Computational Fluid Dynamics (CFD) simulations are performed on a vessel model at leeway angles ranging from 0 degrees to 10 degrees, across a range of regular head wave frequencies and two Froude numbers (0.194 and 0.246). The CFD results are compared with experimental data, showing an average difference of 5.65% under regular wave conditions and 1.63% under calm water conditions. The results indicate that increasing the leeway angle consistently increases the total resistance in both calm water and wave conditions. The added wave resistance coefficient (sigma AW) increases markedly with leeway angle, particularly at a wavelength ratio (lambda/Lwl) of approximately 1.6. The zeroth-order harmonic, corresponding to the mean value of the heave motion, is also strongly affected by leeway, whereas the influence of leeway on the first-order harmonics, representing the oscillation amplitudes of pitch and heave motions, is relatively small. The results further demonstrate that the combined action of leeway and waves leads to an increase in added resistance that exceeds the linear superposition of leeway-induced resistance and waveinduced resistance considered separately.