This work demonstrates a hydrogen (H₂) sensor composed of a tapered optical fiber coated with polyaniline (PANI) nanofibers that operates at room temperature. A transducing platform was fabricated using multimode optical fiber (MMF) with cladding and core diameters of 125 µm and 62.5 µm, respectively. To enhance the light evanescent field surrounding the fiber, it was tapered from the diameter of 125 µm to a waist diameter of 20 µm, a waist-length of 10 mm and coated with PANI using the drop-casting technique. To establish the PANI’s properties, various characterization techniques were applied, such as Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray (EDX), X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The optical properties of PANI layer changes when it is exposed to H₂, leading to a change in the light absorbance. The fabricated sensor was tested by exposing it to H₂ at different concentrations of 0.125% to 1.00%. In this case, the sensitivity, response and recovery times were 15.928/vol%, 110 s and 160 s, respectively. Owing to its room temperature operation, the developed hydrogen sensor is promising for environmental and industrial applications.