Microalgal-bacterial granular sludge (MBGS) is a sustainable biotechnology that has attracted increasing attention, but there remains limited knowledge about the utilization of residual sludge generated from MBGS. This present work proposed a promising approach to rapidly construct the MBGS system from activated sludge by inoculating residual microalgal-bacterial sludge. Compared with inoculated activated sludge, the newly formed MBGS maintained a stable structure, higher biomass content (4.51 g/L), better settleability (42 mL/g), and higher pollutant removal. The results indicated that inoculation of residual sludge resulted in higher extracellular polymeric substances (EPS) content and promoted the microbial aggregation. Besides, this increase effectively improved the electron transfer efficiency within the particle, which facilitated the granulation of MBGS. Microbial community analysis revealed that the dominant bacteria (Pseudofulvimonas and Thauera) were mainly responsible for the secretion of EPS. Furthermore, the nitrogen and phosphorus metabolic pathways were also promoted to some certain extent. In conclusion, the inoculation of residual sludge can achieve an effective reduction in granulation period. This study provides a novel insight and fills the gap in the utilization of residual sludge generated by MBGS.