The additively manufactured (AM) AlSi10Mg aluminum alloy exhibits highly anisotropic microstructures that depend on process parameters and build orientation design. The process optimization and part-building orientations influence the mechanical properties of the materials. In this investigation, we studied the influence of build orientation, such as 0°, 60°, and 90° relative to the build platform, on the crystalline deformation mechanisms of AM-processed AlSi10Mg. We used the X-ray diffraction (XRD) method to characterize the Charpy test specimens. The Charpy test is one of the most popular impact experiments that provides a measurement of the impact energy absorption behavior and toughness of the tested parts. The XRD experiment provides characteristics of the build-orientation-dependent behavior of the Charpy-tested parts. We used the Williamson–Hall method to study the XRD spectrum of the parts produced at different build orientations. The Williamson–Hall (WH) method is one of the renowned methods to investigate the stress–strain behavior of crystals. We used three WH methods, which are known as the uniform deformation model (UDM), the uniform stress deformation model (USDM), and the uniform deformation energy density model (UDEDM), for studying the crystal size, lattice stress, and strain. The results demonstrate that XRD is a powerful tool for finding the fundamental relationships between the additive manufacturing process parameters and the resulting crystal lattice integrity. It also provides crucial insights for the process optimization and mechanical performance prediction of AlSi10Mg components. We found that the 0° (horizontal) samples exhibited different deformation behavior compared to the 60° and 90° (vertical) samples, which correlates with the previously reported mechanical anisotropy of the materials.