Thin-walled composite structures operating in the post-buckling regime needs a thorough understanding of their stability behavior and failure mechanisms. For the accurate prediction of the collapse loads, one needs to account for the damage evolution precisely. In the current study, we have proposed a unified and generic numerical modeling approach that accounts for both the intra and inter-laminar damage modes in stiffened CFRP panels. A 3D finite element based progressive damage model (PDM) is proposed to simulate the collapse behavior of the single blade stiffened composite (SSC) CFRP panels with and without embedded de-bonding defects under uniaxial compression loading. A user-defined material subroutine based on 3D Hashin failure criteria is developed in Abaqus software to study the evolution of intra-laminar damages in SSC panel. Further, the skin-stiffener bonded interface, the inter-laminar interfaces in the skin, stiffener, including the noodle region, is modeled using the cohesive zone elements to simulate the de-bonding/delamination growth. The stability response and collapse load results obtained using the proposed PDM are compared with the experimental observations. Also, the damage evolution, failure mechanisms, the ultimate load, and the corresponding displacement data obtained from the developed PDM are validated with the experimental estimates. A comprehensive damage assessment involving the ultrasonic C-scans, infrared thermograms, and micrographic study is also carried out to supplement the PDM predictions. Thus, the proposed PDM is generic in terms of damage studies and can be used for investigating the collapse behavior of CFRP panels with multiple stiffeners.