Damage evolution in Carbon/Carbon–Silicon Carbide (C/C–SiC) ceramic matrix composites is critical for structural design applications. While C/C–SiC consists of multiple phases, its mechanical performance is primarily governed by carbon fibres and the carbon matrix. This study examines the hypothesis that damage within the carbon matrix drives the overall non-linear mechanical response under tension. A multi-scale hierarchical numerical framework is developed to evaluate the effects of carbon matrix damage across material scales. The Parametric High-Fidelity Generalized Method of Cells (PHFGMC) analyses the periodic microstructure of C/C–SiC. Due to material complexity, a single repeated unit cell (RUC) cannot adequately capture composite behavior. Instead, several distinct RUCs are constructed and nested together to represent microstructural features from the C/C micro-level to the 8-harness ply architecture. This modeling approach systematically assesses how carbon matrix damage influence propagates across structural scales, successfully reproducing experimental tensile response. The framework quantifies individual phase contributions to overall composite properties and establishes a foundation for linking processing characteristics to final material performance, advancing predictive design capabilities for C/C–SiC structural applications.