The global energy crisis has stimulated the development of various forms of green energy technology such as microbial fuel cells (MFCs) that can be applied synergistically and simultaneously toward wastewater treatment and bioenergy generation. This is because electricigens in wastewater can act as catalysts for destroying organic pollutants to produce bioelectricity through bacterial metabolism. In this review, the factors affecting energy production are discussed to help optimize MFC processes with respect to design (e.g., single, double, stacked, up-flow, sediment, photosynthetic, and microbial electrolysis cells) and operational conditions/parameters (e.g., cell potential, microorganisms, substrate (in wastewater), pH, temperature, salinity, external resistance, and shear stress). The significance of electron transfer mechanisms and microbial metabolism is also described to pursue the maximum generation of power by MFCs. Technically, the generation of power by MFCs is still a significant challenge for real-world applications due to the difficulties in balancing between harvesting efficiency and upscaling of the system. This review summarizes various techniques used for MFC-based energy harvesting systems. This study aims to help narrow such gaps in their practical applications. Further, it is also expected to give insights into the upscaling of MFC technology while assisting environmental scientists to gain a better understanding on this energy harvesting approach.