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As a durable and renewable fuel, hydrogen has attracted a huge amount of global interest in its production via different routes. Among these methods, the electrocatalytic hydrogen evolution reaction (HER) is one of the most promising ways for low-cost hydrogen production in the future. In this work, a simple redox hydrothermal method has been developed to fabricate a noble-metal-free MoO2/rGO composite for a highly efficient HER. GO nanosheets provide oxygen-containing functional groups for precursor attachment, and restrict growth of MoO2 nanoparticles (NPs) with a small size due to the space confinement effect among GO layers as well. Benefitting from a synergistic effect between metallic MoO2 NPs and graphene, the obtained MoO2/rGO composite exhibits excellent HER activity with a small onset overpotential of 190 mV, a large cathodic current density, and a small Tafel slope of 49 mV per decade, while MoO2 NPs or rGO itself is not a very efficient HER catalyst. Additionally, the MoO2/rGO composite displays good stability after 1000 potential cycles under both acidic and alkaline conditions. Dramatically improved HER activity and excellent stability are attributed to small size, more active sites, high conductivity and a synergistic effect of MoO2 NPs and graphene. The development of the MoO2/rGO composite as an enhanced active HER catalyst broadens the members of Mo-based HER catalysts and provides an insight into the design and synthesis of other noble-metal-free materials for the cost-effective and environmentally friendly catalyst in electrochemical hydrogen production.