We report the successful synthesis of NiO nanomaterial by combustion method using Plectranthus amboinicus plant leaves extract. The diffraction pattern and image analysis confirmed the FCC lattice structure for green NiO nanomaterial (g-NONM) with spongy, agglomerated and porous nature. The average energy band gap of g-NONM was found to be 4.10 eV. The electrode made of g-NONM exhibited excellent stability in addition to its good reversibility. The g-NONM showed superior photo-decolarisation results for AO dye solution with 33.95 % dye decolorization at 405 nm. The obtained rate constant k value of g-NONM for AO dye is 0.002933 min −1 . The prepared g-NONM electrode showed a minimum charge-transfer resistance which is possibly due to its high conductivity as supported by electrochemical impedance studies. The NiO electrode also exhibited very high alcohol sensing ability in alkaline medium as revealed during CV measurement. The best part of the study was the fast reply (3 s) of the prepared electrode in sensing the drugs at 1 mM concentration solution. In addition, g-NONM can be easily fabricated into stable electrode material for supercapacitors applications. The results suggested that g-NONM can be an efficient and cheaper material for photocatalytic, sensor and supercapacitor applications.