Composite are prone to failure during operation and that's why vast research had been carried out to develop in-situ sensors and monitoring systems to avoid their catastrophic failure and repairing cost. The aim of this research was to develop a flexible strain sensor wire for real-time damage detection in the composites. This strain sensor wire was developed by depositing conductive silver (Ag) nanoparticles on the surface of nylon (Ny) yarn by electroless plating to achieve the smallest uniform coating without jeopardizing the integrity of each material. The sensitivity of this Ny/Ag strain sensor wire was calculated experimentally and gauge factor (G.F) was found to be in the range of 21–25. Then, Ny/Ag strain sensor wire was inserted in each composite specimen at different position intentionally through the thickness during their fabrication depending upon the type of damage to detect. The specimens were subjected to flexural deflection using a 3-point bend test at the strain rate of 2 mm/min. Overall mechanical response of composite specimens and electrical response signal of the Ny/Ag strain sensor wire showed good reproducibility in results however, Ny/Ag sensor showed a specific change in resistance in each specimen because of their respective position. The sensor wire designed, did not only monitor the change in the mechanical behavior of the specimen until final fracture but also identified the type of damage whether it was compressive, tensile or both. This sensor wire showed good potential as a flexible reinforcement in composite materials for in-situ SHM applications before it can become fatal.