Fibre-reinforced polymers (FRP) strengthening can be applied to decrease the seismic vulnerability of existing masonry buildings, both with regard to in-plane and out-of-plane failure mechanisms. Experimentally, the impact of strengthening solutions has been thoroughly studied. There are, however, few efficient and reliable numerical modeling approaches that can accurately capture the effect of such strengthening on the seismic response of the masonry building. Therefore, we herein develop and validate a modeling approach to capture the effect of FRP strengthening on the behaviour of masonry walls. To model this effect, we use a recently developed macro- element, which can capture both in-plane and out-of-plane failure modes. In the macro-element, the intervention is modelled by adding fibres representing the longitudinal FRP strips to the section model. These fibres were modelled as linear elastic in tension up to the failure with a zero compressive strength. Transversal FRP strips effect the shear strength, and in the macro-element, this is accounted for by increasing the cohesion in the equation for the shear strength. To validate the model, we also compare the numerical simulations with existing experimental results obtained from the literature. Overall, the proposed modeling approach accurately predicts the in-plane and out-of-plane response, implying that equivalent frame models can predict the response of masonry buildings with FRP-strengthened walls. To conclude, the models described in this paper can be used for a time- efficient assessment. Moreover, it can help in selecting the optimal strengthening approach for future retrofitting. This aspect is especially important for the cultural heritage structures, where excessive retrofitting should be avoided.