Traditional cementation technique is insufficient in making municipal solid waste incineration (MSWI) fly ashes meet the permissible leaching threshold. Aluminum supplementation and electrokinetic (EK) activation were combinedly incorporated into the traditional solidification pathway to enhance the geopolymerization and the immobilization of Pb and Cd in MSWI fly ashes in this study. The aluminum addition remarkably affected the geopolymer formation. The minimum toxicity leaching as well as the maximum compressive strength were achieved at the combination of the voltage gradient of 1.0 V/cm, the proposing time of 48 or 72 h, the mass ratio of alkali activator to fly ash of 11.5%, and the modulus of 2.1. Chloride reduction in the mortar obtained during the EK process increased the negative charge relativity of oligomers. The leaching concentrations of Pb and Cd from the geopolymer were successfully predicted by a linear model based on the compressive strengths at 28 d. Higher reaction degree was found in the EK-activated mortar in the geopolymerization kinetics. Aluminum supplementation had induced the production of some amorphous aluminosilicate minerals including AlSiO, CaAlSiO·4HO, CaAl(SiO)OH, CaAl(OH)·3HO, and CaAlOCl·10HO during the EK process. Larger particles observed in the EK-treated specimen directly verified the EK-activated pozzolanic reactions.