This work demonstrates a hydrogen (H2) sensor at room temperature made of tapered optical fibers coated with a polyaniline (PANI) nanofiber. A transducing platform was constructed using a multimode optical fiber (MMF) with a 125 µm cladding and a 62.5 µm core diameter. In order to enhance the light evanescent field surrounding the fiber, the fibers were tapered from 125 µm in diameter to 20 µm in diameter with 10 mm waist and coated PANI using the drop casting technique. Various characterization techniques, such as field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), differential X-ray (XRD), and atomic force microscopy, have been used to establish the PANI’s properties. When H2 is subtracted, the optical properties of the PANI layer change, resulting in a change in light absorption. The fabricated sensor was tested by exposing it to H2 at different concentration from 0.125% to 1%. In this case, the sensitivity, response, and recovery times were 15.928/vol%, 110 s, and 160 s, respectively. The improved hydrogen sensor holds great promise for environmental and industrial applications due to its ability to operate at room temperature.