This study investigates the effect of strengthening slender shear walls using FRP composite materials under monotonic loading. Approximately 25 numerical models were developed in ABAQUS to evaluate the nonlinear behavior of slender walls, including cracking, reinforcement yielding, and ultimate failure, while accounting for the confinement effects of FRP. The results indicate that strengthening weak walls with a single FRP layer increased load-bearing capacity by up to 25% and improved ductility by up to 40%. In walls with reduced transverse reinforcement in boundary elements, ductility was up to 30% lower compared to walls with proper seismic detailing, highlighting the critical role of these reinforcements in seismic performance. Additionally, the application of FRP to walls with proper seismic detailing showed minimal impact on load-bearing capacity but improved ductility by approximately 15%. In terms of strengthening configuration, wrapping FRP around the entire wall increased load-bearing capacity by up to 20%, though it was less effective than strengthening only the boundary elements, particularly in walls with proper seismic designs. Furthermore, FRP had little impact on increasing the yield strength of reinforcement but significantly enhanced post-yield behavior and energy absorption capacity of the walls.