Masonry walls are structural elements generally used in housing or small buildings. Given their structural configuration, they commonly present shear failure due to seismic actions, characterized by a fragile response. Thus, it is important to have simple, yet reliable tools that correctly estimate the shear capacity of walls. For that, a simple existing model developed for reinforced concrete elements and based on a panel model is used and adapted to masonry walls, providing a novel formulation that can be applicable to both materials. For compression and tension behavior, the prismatic resistance of the panel is used, which, due to the anisotropy of the material, degrades with the angle formed by the load with the vertical mortar joint. Strain values are set for compression and tension failure modes, and a degradation coefficient in compression due to the biaxial strain loading is included. Additionally, bond failure is also incorporated into the model. A database of 41 tests of reinforced masonry walls and 12 tests of confined masonry walls is used for model validation. The strength ratio between the shear strength obtained by the model and the test is compared, giving an average and a coefficient of variation (COV) of 1.0 and 0.15, respectively for reinforced walls, and 1.08 and 0.14 for confined walls, showing a satisfactory performance and better behavior than simple models from the literature. The analysis of general trends of the strength ratio reveals that there is a low dependence between the strength ratio and the studied parameters, implying that the model captures the physical behavior of masonry walls.