In this article, the Carrera Unified Formulation and full Green–Lagrange nonlinear relations are employed to investigate the postbuckling behavior of laminated composite panels subjected to in-plane shear and combined loadings. The layerwise refined plate models are implemented by the efficient Lagrange expansion functions through the laminate thickness. An artificial surrounding area is assumed to model shear conditions. The accuracy of the presented model is validated based on the available literature. Then, the effects of stiffeners on the nonlinear response of panels are evaluated, and comprehensive assessments are provided for the equilibrium curves and stress distributions.