Electroactive biofilms (EABs) are essential for bioelectrochemical systems, however, the formation of cathodic EABs is more time-consuming than anodic EABs. This study aims to evaluate whether acyl-homoserine lactones (AHLs) could facilitate the start-up of cathodic Geobacter soli EABs. With AHL addition, the biomass, cell viability, and extracellular polymeric substance (EPS) abundance of cathode-associated G. soli EABs were increased. Likewise, redox activities of EPS and outermost proteins in the cathodic EABs were enhanced in the presence of AHLs, which consequently led to better start-up performance of biofilms. Compared to the control without AHLs, start-up lag periods were reduced by approximately 50%, electron uptakes were enhanced by 1.3-2.0 times, and denitrification rates were more than doubled with AHL addition in the start-up cycle, which were comparable to those of mature G. soli cathodic EABs. These findings open up an opportunity for accelerating the start-up of cathodic biofilms via AHLs.