Over the past few years, most applications in the field of light sensing have required devices able to detect light intensities as low as pW/cm ² . At the same time, the rise of organic-based sensors is meeting no stops because of the desired properties that organic materials provide, like flexibility, lightweight, low cost, and low temperature processability. Low-intensity light signal detectors are growing in a huge number of fields. In prostate cancer treatment, modern proton therapy requires the detection of very low light intensities generated by scintillators that convert the proton flux into a light signal; moreover, in robotics, the most recent products need to detect light both in the sunlight and at nighttime, when the illumination intensity is lower. Here, we report on a flexible organic phototransistor (OPT) with impressive low-light detection, with a limit of detection (LoD) down to 28 pW/cm ² . The OPT works reliably in different environments, acting at low polarization bias down to −1 V. These results show the perspective of a new class of light detectors based on a low-cost manufacturing process for flexible applications.