A series of nitrogen doped TiO2/Graphene/Au (N-TiO2/G/Au) and nitrogen doped TiO2/Graphene/Ag (N-TiO2/G/Au) modified nanocomposite electrodes were prepared by a simple electrophoretic deposition method to assess their visible light photo-electro catalytic and photo-electro catalytic ozonation activities against diazinon. The structural and morphological analyses of the synthesized composites were made by XRD, SEM and EDX while the optical properties were studied by DRS technique. The effect of Au and Ag ratio to N-TiO2, Na2SO4 concentration, voltage and initial pH of the solution was optimized by Taguchi method on the degradation of diazinon using photo-electro catalytic process. High degradation 76.7% for N-TiO2/G/Au and 81.1% for N-TiO2/G/Ag was observed when Au and Ag ratio to N-TiO2 was 0.2 wt%, Na2SO4 concentration = 56 mM, voltage = 900 my and pH = 6 after 60 min visible light irradiation. The main intermediates of diazinon degradation were identified using GC-MS spectrometry. Finally, the visible light photo-electro catalytic ozonation of diazinon using optimized nanocomposites were studied. The results demonstrate that the photo-electro catalytic ozonation highly enhanced the degradation rate of diazinon (nearly 100%) compared to photo-electro catalytic and ozonation processes, solely. Also, nanocomposites showedy good catalytic activities even after seven successive degradation cycles.