<p>Fault Damage Zones (FDZs) developed from neo-tectonic stresses and shear displacement, acting as crucial corridors where rock masses experience significant mechanical deterioration, affecting slope stability and landslide development. This study investigates how faulting affects rock mass characteristics and slope stability in the Hanzel fault damage zone (FDZ) in Pakistan’s Northwestern Himalayas. Rock mass geometrical properties, such as volumetric joint count (<i>Jv</i>), joint spacing (<i>Js</i>), joint persistence (<i>Jp</i>), and normalized block size (<i>RQD/Jn</i>), as well as rock mass quality (rock quality designation, or <i>RQD</i>; geological strength index, or <i>GSI</i>), and shear strength (cohesion and the internal friction angle) were analyzed across the FDZ. We demonstrate heterogeneous rock mass degradation from the fault core to the FDZ edge, driven by tectonic stress, diverse metamorphic lithologies, and multiple geological structures (such as schistosity/foliations, joint sets, and shear zones) formed throughout the evolutionary history of the fault. A clear relationship between fault-induced deformation and rock mass quality demonstrates that the tectonic evolution significantly influences shear strength parameters and rock mass stability. The slope failure modes (2.73–39.36% critical intersections) and increased landslide susceptibility (67%) are notably concentrated near Intense Deformation Zones (IDZs), as confirmed by the kinematic analysis, geospatial, and statistical evaluation of landslides. Using an integrated approach, this study provides the first macro-scale FDZ characterization in the Himalayas, offering a predictive framework for landslide hazards (e.g., threshold width: 3.9 ± 0.2&#xa0;km). Our research findings have broader implications for real-time monitoring and sustainable engineering practices for mitigating geohazards along or across FDZs in tectonically active areas.</p>