The use of solar energy to activate chemical pathways in a sustainable manner drives the development in photocatalysis. While catalyst optimization is a major theme in this pursuit, the development of novel photocatalytic reactors to enhance productivity is also imperative. In this work we combine, for the first time, microstructured optical fiber technology with photocatalysis, creating a photocatalytic microreactor coated with TiO2, decorated with palladium nanoparticles. In doing so, we create a system capable of effectively combining photons, liquids, and gases within a monolithic, highly confined, transparent silica geometry. We utilize a range of characterization techniques to selectively focus on the photocatalyst, that resides exclusively within the internal capillaries of this system. In doing so, we validate our design approach and demonstrate the ability to simultaneously control both nanoparticle size and metal content. Further, we justify our unique design, showing its activity in photocatalytic hydrogen generation from water. In doing so highlights the importance in developing light propagation properties from optical fibers and the significant potential of this technology in the expansive photocatalysis landscape.