Out-of-plane failure of masonry walls is often responsible for the partial collapse of unreinforced masonry structures. Modeling the out-of-plane response of these walls is therefore key in the assessment of existing buildings. The paper presents a new trilinear model describing the force-displacement response of vertically spanning unreinforced masonry walls subjected to out-of-plane loading. Different factors that affect the response of the walls are captured by the model: the support conditions, the level of applied axial load, the slenderness ratio, and the deformability of the wall. The model is validated against experimental results from shake table tests. The force and displacement parameters of the model are described by analytical expressions that are derived from a mechanical model previously developed for unreinforced masonry. They offer an alternative to existing trilinear models in which corner displacements are mainly defined by empirical relationships.