Here the synthesis and the optimization of piezoelectric materials by varying the reduced graphene oxide (RGO) contents in the poly(vinylidenefluoride-trifluoroethylene)-0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3(P(VDF-TrFE)-PMN-PT) composite and their application to low-pressure and low-frequency energy harvesting have been reported. Among the synthesized piezoelectric compositions, the PPMR5 (P(VDF-TrFE)-PMN-PT-RGO (RGO = 0.5%)) sample exhibits a maximum dielectric constant of 60 and a relatively high dielectric loss of 0.0654 at 1 kHz. Additionally, flexible piezoelectric energy harvester (FPEH) made off PPMR5 sheet reveals highest output performance under mechanical deformation. The fabricated FPEH demonstrate a maximum open-circuit output voltage of 8 V(pk-pk) and a short-circuit current of 3.5 μA(pk-pk) at an external applied force of 2N. Furthermore, the FPEH exhibits an output power density of 6.5 μW/cm2 at 1 MΩ load resistance. The fabricated device was also exposed to several pressing-releasing cycles to confirm its stability. The device shows excellent stability even after 1000 pressing-releasing cycles. Finally, our fabricated FPEH can be a promising energy source for futuristic flexible electronics.