Polymer matrix composites (PMCs) are being used in the aerospace industry owing to their good stiffness, high strength-to-weight ratio, and resistance to fatigue and corrosion. However, these structures are vulnerable to impact-induced damages. These damages are barely visible on the impact surface due to the anisotropic nature of this material, while they may be significant in other areas. It is generally uneconomical to inspect these structures by regular non-destructive testing (NDT) methods, and hence smart sensors are being developed for the health monitoring of these structures. The advances in the field of nano-scale conductive fillers such as carbon nanotubes (CNT) and graphene have led to the development of electrically conductive smart PMCs. In the present work, a spray deposited graphene nanoplatelet(GNP)/Polymethylmethacrylate(PMMA) smart layer on a glass fiber reinforced polymer (GFRP) composite specimen is used as a sensor to monitor the strain and studied its performance under various practical loading conditions. The piezoresistive behavior of these sensors was evaluated in monotonic, step, and cyclic loading conditions. These spray-coated sensors offered good sensitivity (38.5 times) as compared to a strain gauge. It was also observed that GNP spray coats with different number densities can be tailored according to the applications such as a high emissivity surface to create a visible thermal contrast, to increase the signal-to-noise ratio in Infrared thermography(IRT) or for thermal management in the automotive and aerospace applications. The ease in the process of application coupled with good sensitivity demonstrates that the GNP/PMMA spray-coated sensor can be a potential candidate for the futuristic multi-functional materials for structural health monitoring.