Laser Shock Peening is a well-known surface treatment technique able to introduce compressive residual stress on metal components. This is recognized to be very effective in increasing the fatigue life, the resistance to fretting fatigue and the resistance to stress corrosion cracking. Compared to the more conventional shot peening process, a deeper compressive residual stress field and a better surface finish can be generally achieved. This research is focused on the application of laser shock peening over middle crack tension specimens M(T), mainly representative of aircraft wing lower covers. These structural components are principally designed to fulfil fatigue criteria, therefore improving their fatigue and damage tolerance performance can lead to either less maintenance or weight saving. Several specimen sizes and laser peening configurations were studied to understand their effect on residual stress, fatigue life and crack growth rate. The treated areas were also applied at different distances from the central crack notch, to evaluate the effectiveness of laser peening on slowing down crack propagation for different crack lengths. Extensive residual stress measurements were carried out with diffraction techniques, incremental hole drilling and the contour method, to achieve a complete picture of the 3D residual stress distribution within the specimens. Constant amplitude fatigue testing was realised with two different stress ratios, to assess the influence of different loading conditions on fatigue performance. Results showed that laser shock peening increased the fatigue life of unpeened samples up to 4 times and a fully compressive residual stress profile through the thickness was achieved along the crack opening direction. Fatigue lives and crack growth rates were predicted with a linear elastic finite element model, obtaining a very good correlation with the experimental data. A parametric analysis was also run, which allowed finding an optimal configuration to maximise the fatigue performance.