We employ first-principles density functional theory (DFT) simulations to study the potential of BCN monolayer as a promising hydrogen (H2) storage material. Van der Waals corrected simulations reveal that selected light metals bind to defected BCN with strong binding energies of − 3.41, − 2.52, − 2.93, − 2.27, and − 4.24 eV for Li, Na, K, Mg, and Ca, respectively. Such strong bindings reduce the inclination of metal dopants to form clusters over the BCN surface. Charge analysis indicates that metal dopants attain cationic characters by donating their valence electrons to BCN, facilitating the adsorption incident H2 molecules through polarization and electrostatic interactions. A maximum of 16H2 molecules could be adsorbed to metal-doped BCN, resulting in significantly high gravimetric densities of 10.10, 9.18, 8.41, 9.11, and 8.36 wt% for 2Li-, 2Na-, 2 K-, 2 Mg-, and 2Ca-BCN, respectively, comfortably exceeding the 5.50 wt% target set by the US Department of Energy (DOE). Furthermore, statistical thermodynamic analysis based on the Langmuir model is applied to study the H2 storage capacity under ambient temperature and pressure conditions. Under practical conditions, adsorption at 30 atm/ 300 K and desorption at 3 atm/375 K, the maximal reversible H2 storage capacities of metal-doped BCN systems fall in the range of 6.30–8.70 wt%. We believe that our findings can pave the way for the development of highperformance BCN-based H2 storage materials.