Effective techniques to reduce graphene oxide are in demand owing to the multitude of potential applications of this two-dimensional material. A very promising green method to do so is by exposure to ultraviolet irradiation. Unfortunately, the dynamics behind this reduction remain unclear. Here we perform a series of transient absorption experiments in an effort to develop and understand this process on a fundamental level. An ultrafast photoinduced chain reaction is observed to be responsible for the graphene oxide reduction. The reaction is initiated using a femtosecond ultraviolet pulse that photoionizes the solvent, liberating solvated electrons, which trigger the reduction. The present study reaches the fundamental time scale of the ultraviolet photoreduction in solution, which is revealed to be in the picosecond regime.