The rational design of a sustainable synthetic pathway to develop carbonaceous materials with efficient electrocatalytic activity for energy conversion is a great challenge. Herein, a one-pot method has been applied to synthesize metal–organic framework and polymer nanocomposites (MOF@polymer) with well controlled features, which can be used as a carbon source to produce metal-entrapped, nitrogen-doped mesoporous carbon materials for hydrogen evolution. Specifically, zeolitic imidazolate framework-67 (ZIF-67) was firstly crystallized in 2-methylimidazol aqueous solution, and then green phenolic resin (RF) from phloroglucinol–glyoxylic acid and a catalyst/nitrogen source (triethylenediamine) was co-condensed on the surface of the ZIF-67 crystal in the same system. Then, the obtained ZIF-67@RF nanocomposite transformed into cobalt-entrapped nitrogen-doped mesoporous carbon (Co-NC). Taking the advantages of the cobalt-based electroactive phases, abundant Co–N–C species and the unique porous structure, Co-NCs manifested excellent hydrogen evolution catalytic activity (had an onset overpotential of −45 mV and a small Tafel slope of 65 mV dec⁻¹, in 0.5 M H₂SO₄ solution) with good stability.