<p>Photodetectors and hydrogen sensors are conventionally devised as separate structures, which selectively respond to optical or gaseous stimuli. Hydrogen detection is vital for safety and energy use. Traditional sensors based on metal oxide or palladium are slow and less selective and sensitive to environmental conditions. Hybrid photodetector–hydrogen sensors address these challenges by combining hydrogen-sensitive nanomaterials, such as palladium alloys, conducting polymers, and graphene, with photonic elements like micro-ring resonators and optical fibers. Tungsten oxide (WO₃) is a multifaceted transition metal oxide (TMO) characterized by its notable properties of gasochromism, a wide bandgap, and high photocatalytic activity, all of which are beneficial for the development of WO₃-based hybrid photodetectors and hydrogen sensors. This review article presents a comprehensive overview of WO₃-based hybrid photodetectors and hydrogen sensors for multifunctional sensing applications. Furthermore, it highlights the significance of WO₃ and its nanostructures in enhancing the performance of the WO₃-based hybrid photodetector–hydrogen sensor, as well as how modifications in WO₃ nanostructures can lead to future developments in WO₃-based hybrid photodetector–hydrogen sensors.</p>