Graphitic carbon nitride (g-C3N4) and its composites for the hydrogen evolution reaction (HER) have gained immense attention owing to their facile synthesis technique and favorable catalytic performance. Herein we present a composite prepared using a g-C3N4 and H3PW12O40 polyoxometalate (POM) electrocatalyst synthesized by a novel approach for HER application. The electrocatalyst is synthesized by the complexation of a tailored POM, i.e. Ru-substituted polyoxometalate (PW11Ru), with melamine followed by calcination under an inert atmosphere. The proposed monomer complexation strategy utilizing well-defined modulated PW11Ru as a metal precursor provided a unique approach for the preparation of a highly dispersed matrix to form a RuW/g-C3N4 composite. The HER activity of the obtained RuW/g-C3N4 composite is evaluated and compared with individual components of composites by performing several control experiments. RuW/g-C3N4 exhibited improved electrochemical activity towards the HER with an overpotential of approximately 266 mV at 10 mA cm−2 with a Tafel slope of 63 mV dec−1. This new approach using tailored-transition-metal substituted POMs and melamine as the monomer precursors will be expected to contribute to the development of well-defined cluster-embedded 2D-carbon materials with enhanced electrochemical activities. © 2024 RSC.