The dense passive film on 316L stainless steel is the key in its corrosion resistance. Its interactions with an electroactive biofilm are critical in deciphering microbial corrosion. Herein, an in-depth investigation using genetic manipulations and addition of an exogenous electron mediator found that extracellular electron transfer (EET) mediated by the electroactive S. oneidensis biofilm grown aerobically accelerated the destruction of the microstructure and weakened the passive film. The changes in surface properties accelerated the electrochemical reactions and increased pitting corrosion. The redox state on the surface also changed due to the activity of the electroactive biofilm. A synergistic EET corrosion mechanism, including both direct and mediated electron transfer with passive film destruction was proposed to illustrate the corrosion caused by electroactive S. oneidensis. The techniques used in this work provide a systematic approach to probe EET impact on microbial corrosion by electroactive biofilms with electron transfer across the biotic-abiotic interfaces.