Graphene-based nanocomposites have attracted a tremendous attention, showing excellent performance in energy conversion applications, such as reduction of carbon dioxide and hydrogen evolution reaction (HER). Herein, a study on in situ generation Cu nanoparticles on reduced graphene oxide (rGO/Cu) by reducing simultaneously both graphene oxide and Cu2+ ions during the biphasic HER by organic sacrificial agent decamethylferrocene (DMFc) was reported. The in situ-generated rGO/Cu catalyst was morphologically and structurally characterized by microscopic and spectroscopic techniques, respectively. The hydrogen evolution catalytic activity of rGO/Cu was investigated by using 4-electrode voltammetry and two-phase reaction methods. rGO/Cu nanocomposite catalyst displayed a better catalytic activity than the non-catalyzed reaction and free-Cu catalyst by enhancing the HER rate approximately 208- and 3-times, respectively. The HER activity of rGO/Cu gave results comparable to the noble metallic and the other nanocomposite catalysts such as Pt, Pd, MoSx and their nanocomposites with carbon-based materials.