Laser Shock Peening (LSP) enables the generation and modification of residual stresses deep below the surface of metallic components. LSP-induced residual stress profiles provide penetration depths of compressive residual stresses in mm range, which can be used to retard the fatigue crack propagation (FCP) within thin sheets. These compressive residual stresses may lead to crack closure at significant applied tensile loads. This crack closure phenomenon is assumed to be one of the dominant mechanisms to reduce the load range at the crack tip, resulting in a fatigue crack retardation. This work provides an experimental and numerical investigation of the FCP in AA6056 based on C(T)100 specimens. Residual stresses were introduced by two-sided LSP treatment of the sheet material. The resulting residual stresses were determined by the incremental hole drilling method with electronic speckle pattern interferometry. The residual stress measurements on both sides of the specimens reveal differences of the residual stresses due to the laser shock peening process design. The occurrence of crack closure was evaluated by crack opening displacement vs. load curves, which can be used to determine the crack opening force. A multi-step simulation is applied to predict the residual stress field, the stress intensity factor range and rate if residual and applied stresses are present simultaneously as well as the FCP rate. Numerical predictions and measurements of the FCP rates are in excellent agreement.