Over the past few years, composite steel–concrete beams saw numerous applications in bridge construction because of their competitive cost in comparison with non-composite steel or reinforced concrete structures. Bridges, in particular and industrial structures in general, are commonly subjected to cyclic loading of vehicles or operating machines. This made it important to study and investigate the behavior of composite structures under fatigue. In this study, the cyclic loading behavior of simply supported composite beams was analyzed numerically using ANSYS finite element software. Following analysis validation using the experimental literature load–deformation results, the numerical models were used in a parametric study to investigate the response under cyclic loading to varying degree of shear connection between the beam’s concrete slab and steel section. According to finite element simulation results, there was consistent compatibility in terms of stiffness changes with fatigue life, low deflection values, increased fatigue life and a clear delay in reaching the failure under achieving more than 80% of composite action in order to have the optimum performance under fatigue loading. Shear lag phenomenon— which is a good indication of the continuity in strain between concrete slab and steel beam—was also observed, and it had an influence effect on studying the weld region between shear connectors’ body as a target element and top flange of the steel beam in order to achieve the required degree of composite action.