This study investigates the effects of temperature and humidity on fibre-reinforced polymer (FRP) retrofitted masonry structures bonded with epoxy adhesive. Although FRP strengthening is widely used, there is limited understanding of how moisture and temperature jointly influence the adhesive and overall system performance. To address this gap, a series of experiments was conducted using Class A engineering bricks bonded with FRP sheets under controlled environmental conditions: temperatures of 10  \(^\circ \) C, 25  \(^\circ \) C, and 50  \(^\circ \) C, and relative humidity levels of 30%, 50%, 70%, and 90%. The specimens were conditioned for 48 h both before and after bonding, followed by pull-out tests to assess bond performance. The results show that maximum load capacity was achieved at 25  \(^\circ \) C and humidity levels below 70%. However, under extreme conditions (50  \(^\circ \) C and 90% humidity), the load capacity dropped to approximately one-sixth of the maximum value, demonstrating the substantial impact of environmental conditions on the long-term effectiveness of FRP-retrofitted masonry systems.