Fatigue performance of nickel-based superalloys such as Inconel 718 is a critical issue in safety-critical applications, particularly in aerospace components subjected to severe cyclic loading and harsh operating environments. Fatigue crack initiation in these materials is strongly influenced by microstructural and geometrical defects, including surface roughness and internal gas porosities, which act as stress concentrators and significantly reduce fatigue life. Accurate modeling of fatigue damage evolution in the presence of such defects remains a challenging task for conventional continuum-based methods. In this study, a peridynamic framework [1] is employed to investigate fatigue crack initiation in Inconel 718 under cyclic loading conditions. The nonlocal nature of peridynamics enables a unified treatment of crack nucleation without the need for additional crack tracking criteria. Surface roughness and porosity defects are explicitly incorporated into the numerical model to assess their influence on fatigue damage evolution and lifetime reduction. The numerical results demonstrate that both surface roughness and internal porosities have a pronounced effect on fatigue crack initiation sites, and overall fatigue life. Increased defect severity leads to earlier crack initiation and accelerated damage evolution. The peridynamic framework demonstrates strong capability in capturing defect-driven fatigue mechanisms and provides physically consistent predictions of fatigue behavior in Inconel 718. The results further reveal that interactions between surface roughness and porosity defects lead to a significant reduction in fatigue life, highlighting the importance of considering combined defect effects in fatigue assessments of metallic materials.