Here we propose a simple and facile route to synthesize a high-performance composite electrode material (PMG composite) for next-generation supercapacitor through in-situ polymerization of aniline in the presence of molybdenum trioxide (MoO3) and graphene nanoplatelets (GNP). Its structure and bonding were studied with Fourier transform infrared (FTIR) spectroscopy, wide angle X-ray diffraction (WAXD) and Raman spectroscopy. Morphological analysis (Field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM)) revealed the coating of fibrillar PANI on MoO3/GNP composite. The prepared composite electrode material is semiconducting in nature as indicated from its non-linear current (I)-voltage (V) characteristics. Most importantly, this PMG composite showed significantly large specific capacitance of ≈593 F/g at the current density of 1 A/g with outstanding cyclic stability (with 92.4% retention of the original specific capacitance even after 1000 cycles) and 734 F/g at 10mV/s scan rate indicating the highly availability of the electrode-electrolyte interfacial area for the redox processes by synergistic contributions of the components through mutual interactions facilitating the ionic conduction through the constituents. Moreover, applicability of the PMG composite as the high-power energy resource in acidic electrolyte is accomplished as it shows excellent energy density along with high power density.