Two-dimensional (2D) materials with suitable electronic and optical properties offer various possibilities for photocatalytic applications. Although various 2D materials have hitherto been specified as adequate candidates, materials with high photocatalytic efficiency for water splitting are still minimal. In this study, we predict a 2D Janus GePAs monolayer and examine its capability for photocatalytic water splitting by performing first-principles calculations. The GePAs monolayer is shown to possess robust dynamic and thermal stability. The direct electronic band gap in the visible region and band-edge positions of the strain-free and strained monolayers are revealed to be convenient for redox reactions in wide pH ranges. The low recombination probability of charge carriers ensured by high and anisotropic carrier mobility enhances the material’s photocatalytic potential. Optical response calculations, including many-body interactions, indicate significant optical absorption capacity in the UV-visible range. Furthermore, low exciton binding energy facilitates dissociation into free electrons and holes, promoting photocatalytic reactions. Our study suggests that the GePAs monolayer is an ideal and remarkably promising material to be utilized in visible-light-driven photocatalytic applications.