Herein, an effective electrocatalyst exploiting non-noble metal oxide-containing of manganese oxide (MnO2) supported on graphitic carbon nitride (g-C3N4) for reduction of CO2 over a wide range of potential. The MnO2 decorated g-C3N4 nanocomposite was synthesized by precipitation, followed by calcination to attain uniform distribution of the MnO2. The MnO2 was found alpha-MnO2 crystal structure with a size of similar to 0.5-2 nm having interlinear lattice spacing of 0.243 nm seen on the layer of g-C3N4 (50 100 nm). The high defective sites observed on MnO2/g-C3N4 (ID/IG) is 1.91 than pristine g-C3N4 (ID/IG) is 0.054. The core spectrum analysis of XPS showed N, C, O and Mn atoms in the as-synthesized composite. The electrocatalysts were executed for electro-catalytic hydrogenation of CO2 at lower onset potential of 0.14 V vs. RHE into C1 products having Faradaic efficiencies (FE) of 8, 47.45 and 65.28% at an applied potential of 0.14, 0.34 and 0.54 V vs. RHE, respectively. The catalyst has further used for the chemical hydrogenation of CO2, and the good yield of formic acid was 9603.28 mu mol obtained. The enrichment of the electrocatalytic activities was observed due to the synergetic effect of both MnO2 and g-C3N4. This methodology will be applicable for industrial applications and it will help control environmental issues.