Hydrogen evolution by decamethylruthenocene (Cp2RuII) was studied in detail highlighting that metallocenes are capable of photo‐reducing hydrogen without the need of an additional sensitizer. Electrochemical, gas chromatographic and spectroscopic (UV/vis, 1H and 13C NMR) measurements corroborated by density functional theory (DFT) calculations indicate that the production of hydrogen occurs by a two‐step process. First, the decamethylruthenocene hydride ([Cp2RuIV(H)]+) is formed in the presence of an organic acid. Subsequently, [Cp2RuIV(H)]+ is reversibly reduced via a heterolytic reaction with one‐photon excitation leading to a first release of hydrogen. Thereafter, the resultant decamethylruthenocenium ion ([Cp2RuIII]+) is further reduced leading to a second release of hydrogen by deprotonation of a methyl group of [Cp2RuIII]+. Experimental and computational data show the spontaneous conversion of [Cp2RuII] to [Cp2RuIV(H)]+ in the presence of protons. Calculations highlight that the first reduction is endergonic (ΔG0 = 108 kJ·mol−1) and needs an input of energy by light for the reaction to occur. The hydricity of the methyl protons of [Cp2RuII] was also considered.