This experimental study has shown the effectiveness of fiber-reinforced polymer (FRP) external bonding (EB) in enhancing the flexural capacity of reinforced masonry (RM) walls subjected to out-of-plane cyclic load. Twelve reinforced masonry walls were built using fully grouted concrete masonry units. The walls had three different steel reinforcement amounts, 2#3, 2#4, and 1#5, representing typical underreinforced wall sections. The strengthened walls used two FRP types, wet lay-up glass fiber sheet (GFRP) and prefabricated carbon fiber-reinforced polymer laminate (CFRP). Four RM walls without strengthening were used as reference specimens. Six walls were externally strengthened using one and two sheets of GFRP. The remaining walls were strengthened with one and two CFRP laminate. A simple model was developed to predict the FRP debonding strain. Nonlinear analysis can be conducted using the moment-curvature relation. As a result of this study, the proposed model presents an excellent prediction compared to the experimental results. Different modes of failure, including compressive concrete crushing failure, FRP rupture, shear failure, and FRP debonding from the masonry substrate, occurred in the strengthened reinforced walls.