Herein, we report the hydrothermal synthesis of g-C3N4/BiVO4 nanocomposite materials for high-energy and high-operating-voltage supercapattery in aqueous electrolyte. The surface morphology and particle size of the prepared nanocomposite were examined by field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) analyses. From the analyses, the formed rice-pellet-like BiVO4 is uniformly decorated over the g-C3N4 nanosheets. This enhances the wettability of material and leads to easy permeability of electrolyte ions in electrode, which help enhance the specific capacity value. The g-C3N4/BiVO4 (6 wt % of g-C3N4) nanocomposite material exhibited a high specific capacity of 2171 C/g at a current density of 2 A/g in the three-electrode configuration. The symmetric supercapattery device using the g-C3N4/BiVO4 (6 wt % g-C3N4) nanocomposite material delivered high energy and power densities of 61 Wh/kg and 16.2 kW/kg, respectively, in aqueous electrolyte with a maximum operating cell potential of 2 V. It exhibits a very high electrochemical stability of 130% at the current density of 20 A/g over 20 000 cycles with a coulombic efficiency of 98.8%. The superior properties of the device can attribute to the synergistic effect of both capacitive (nonfaradic) and battery-type (noncapacitive) processes in the charge storage mechanism of the nanocomposite material.