The Integrated Thermal Protection System (ITPS) is designed to endure both structural and severe thermal loads acting on the external surfaces of the Reusable Launch Vehicles (RLV). The corrugated core sandwich structures are being considered for ITPS applications due to their superior insulative and structural properties. It can experience significantly varying thermal loads during different phases of flight from ascent to re-entry, resulting in spatially varying temperature-dependent properties and thermal stresses depending on its location on vehicle and operating conditions. Thermomechanical analysis of components such as wing and fuselage along with ITPS panel subjected to varying thermomechanical load is a formidable task as the length-scale of such structures is significantly larger than core geometry of ITPS panel. Thus, analysis becomes infeasible due to exorbitant computational cost. To address this problem, ITPS panel is idealized as an orthotropic plate to enable thermomechanical analysis by homogenizing the response of corrugated core sandwich structure. In this work, homogenization method has been developed to obtain the thermomechanical properties of plate representation of the ITPS panel. The novelty of this approach is the incorporation of through-thickness temperature field in the derivation of the homogenized thermomechanical properties using shear-deformable plate theory. The formulation incorporates the effect of temperature gradient in generic polynomial form and represents the homogenized properties in terms of unknown constants that can be calibrated with unit-cell and beam analyses depending upon the order of polynomial. This formulation can be extended to any higher-order temperature polynomial with additional constants to be calibrated. For demonstration purpose, linear thickness-wise temperature distribution varying along the length is considered for both homogenized plate model and ITPS panel. The efficacy of the proposed method is demonstrated by comparing the homogenized model with full-scale model of ITPS panel subjected to spatially varying temperature field and pressure load. The comparison shows that the derived homogenized plate provides a reasonably accurate and efficient representation of ITPS panel.