Nanotechnology has potential applications in creating self-sensing smart materials. The nanomaterials are used to develop the 3D printed nanocomposites strain sensors that have better mechanical and piezoelectric properties. In the current study, strain sensors are developed by adding carbon fiber and multiwalled carbon nanotube (MWCNT) into epoxy matrix, which acts as a conductive path, and integrated into a polylactic acid (PLA)-based 3D printed composite. Electromechanical tests are performed to assess the piezoelectrical properties of these sensor by applying a gradual increase in mechanical loading, such as flexural testing on the sensor and compression testing on a cube is carried out by embedding theses sensor. A finite element model is developed to evaluate the critical stress between fibre and PLA composites of the sensor. The current study describes a self-sensing piezoresistive sensor capable of monitoring strain in structures. The experimental study demonstrates the integration of nanomaterials with 3D printed specimens, resulting in a promising smart self-sensing strain sensor.