Thermoelectric (TE) fibers have excellent potential for multimodal sensor, which can detect mechanical and thermal stimuli, used in advanced wearable electronics for personalized healthcare system. However, previously reported TE fibers have limitations for use in wearable multimodal sensors due to the following reasons: 1) TE fibers composed of carbon or organic materials have low TE performance to detect thermal variations effectively; 2) TE fibers composed of rigid inorganic materials are not stretchable, limiting their ability to detect mechanical deformation. Herein, the first stretchable TE fiber-based multimodal sensor is developed using copper(I) iodide (CuI), an inorganic TE material, through a novel fabrication method. The dense CuI nanoparticle networks embedded in the fiber allow the sensor to achieve excellent stretchability (maximum tensile strain of ≈835%) and superior TE performance (Seebeck coefficient of ≈203.6 µV K−1) simultaneously. The sensor exhibits remarkable performances in strain sensing (gauge factor of ≈3.89 with tensile strain range of ≈200%) and pressure sensing (pressure resolution of ≈250 Pa with pressure range of ≈84 kPa). Additionally, the sensor enables independent and simultaneous temperature change, tensile strain, and pressure sensing by measuring distinct parameters. It is seamlessly integrated into a smart glove, demonstrating its practical application in wearable technology.