This study presents a computational framework for the nonlinear stability assessment of hybrid three-layer timber beams composed of high-stiffness face layers and a compliant core, with particular emphasis on the influence of geometric imperfections and interface slip on structural performance. The formulation is developed within a variational energy framework based on the principle of minimum total potential energy, incorporating bend-ing, membrane, and interlayer slip effects under large geometric imperfections. An energy-based indicator is further employed to interpret the evolution of structural response from bending-dominated behavior to membrane-influenced behavior under increasing defor-mation. The numerical implementation is carried out using an incremental–iterative proce-dure, enabling efficient parametric investigation of imperfection amplitudes and interface stiffness levels. The results demonstrate that even moderate geometric imperfections can significantly reduce the effective stiffness and modify the load–deflection response, leading to a pronounced knock-down effect in structural stability. In addition, large deflections promote the increasing contribution of membrane action, which influences the post-critical structural response. Parametric analyses are conducted to establish relationships between imperfection magnitude, interface stiffness, and stability limits. The obtained results pro-vide design-oriented insights by identifying practical stability thresholds beyond which conventional linear design approaches may become unconservative. The proposed frame-work therefore offers a computationally efficient tool for the preliminary stability assess-ment and practical evaluation of hybrid timber members.