Fully inorganic metal halide perovskites (MHPs) demonstrate enhanced stability over their organic–inorganic counterparts, however, their integrations into flexible or textile-based substrates remain a significant challenge, due to their inherent rigidity and the necessity of high-temperature annealing. Herein, we propose a one-step and near-room-temperature electrospinning process to fabricate flexible CsPbI2Br nanofibers that can be directly deposited on the yarns. With the in-situ CsPbI2Br crystallization during electrospinning, annealing-free and photoelectroactive γ-CsPbI2Br can be achieved. Polyvinyl acetate (PVAc) serves as the carrier polymer to offer the flexibility and facilitate the chemical interaction with CsPbI2Br, thereby mitigating moisture and oxygen-induced degradations. CsPbI2Br-PVAc nanofibers obtained under the optimal electrospinning condition: high-electrospinning voltage (25 kV) and low-solution supply rate (0.02 mm/min), show more uniform morphology, increased stability, and extended photoluminescence decay time. These nanofibers enable the construction of photo-sensing yarn devices, capable of generating a photovoltage of around 180 mV and current density of 17 mA/cm2 upon illumination by a 532 nm pulsed laser, while maintaining a remarkable ambient stability of 16 days. Given their laser-energy-dependent voltage output, these yarns hold significant potential for developing high-intensity light-detecting textiles for various applications.