The design of a wall under monotonic loading with axial force and in-plane moment is not rigorously covered in current standards. Specifically, most current standards do not provide guidance for considering wall buckling failure under this loading condition in the design process. Buckling occurs when an element is compressed, leading to out-of-plane displacement that causes additional forces (second-order theory). While some standards provide design methods, these are often overly conservative. From a theoretical perspective, this type of failure can occur since part of the wall is under compression. The goal is to propose a design method for walls under combined actions of normal force and in-plane moment. To achieve this, studies using the nonlinear finite element method are conducted to understand the behaviour of walls under this loading. Based on the study results, a design method is proposed. Specifically, using a section analysis, an equivalent column is defined, and a compressive force, derived from the internal equilibrium of the section, is considered. Then, three factors, defined during the study for the development of the design procedure, are applied to achieve the final wall design.