The present study demonstrates the synthesis of ternary composites of zinc vanadate (Zn3V2O8) with silver (Ag) and carbon matrix originated from the Bengal gram bean extract (BGBE) using a facile, economic, and environmentally sustainable rotational chemical bath deposition (R−CBD) method. From the electrochemical studies, it is found that the Zn3V2O8−Ag@C demonstrated improved electrochemical performance with the specific capacitance (Csp) of 380.1 F g−1, energy density (ED) of 52.7 Wh kg−1, with power density (PD) of 882.3 W kg−1 at 3 mA cm−2 current density and good capacitive retention of 89.8 % over 3000 charge–discharge (GCD) cycles, which is remarkably higher than the other electrode materials (Zn3V2O8, Zn3V2O8−Ag, Zn3V2O8@C). The combined merits of conductive silver (Ag) nanoparticle and carbonaceous material from BGBE assist in enhancing the overall electrochemical performance of Zn3V2O8−Ag@C. The Zn3V2O8−Ag@C nanocomposite was used as electrode material for the fabrication of a flexible symmetric solid–state supercapacitor device (SSC). The SSC device delivered a Csp of 69.17 F g−1 with an energy density (ED) of 13.8 Wh kg−1 at a 2 mA cm−2 current density. Moreover, the SSC shows a 90 % capacitive retention over the continuous GCD cycles.