The sensitivity of the photodetector is a crucial parameter when evaluating the performance of a cubic structure-based tin mono-sulfide (SnS) photodetector. However, achieving high sensitivity with a low-cost deposition technique for the SnS photodetector, which is based on a film grown on a flexible substrate, has been challenging. The primary aim of the present research is to fabricate a photodetector with higher sensitivity based on SnS thin film. The film was deposited onto a flexible polyester substrate utilizing a cheap and simple chemical bath deposition (CBD) method under 80 °C, pH 7.4, and 2.5 hours. The X-ray diffraction analysis showed that the film is made up of many small crystals and has a cubic shape, with an energy gap value of 1.56 eV. The photo-response properties were conducted upon illumination of near-infrared (NIR) 750 nm. The findings demonstrated that the photodetector has excellent stability and photo-response characteristics, involving a sensitivity of 1775, a rise time of 0.72 s, and a recovery time of 0.68 s. The fabricated flexible photodetector shows outstanding promise due to its excellent performance, cost-effectiveness, flexibility, and non-toxicity.