Microbially induced calcium carbonate precipitation has been introduced as a novel solution for high-shrinkage cracking of alkali-activated slag (AAS) systems. The high shrinkage rate of AAS is one of the main limitations hindering the full-scale application of AAS composites. AAS shrinkage cracks are micro, inaccessible, and propagate through the section. Hence, incorporating bacteria would be an innovative, autonomous solution for this critical behavior. To the knowledge of this article, the feasibility of bacteria within different AAS alkaline environments has never been addressed or investigated. This study assesses the performance of Bacillus subtilis at various alkali environments of alkali dosage (6% and 8%) and modulus silicate (0.8 and 1.2). The microbial performance was evaluated by examining mechanical characteristics, durability, and cracking behavior. Bacillus subtilis was proved to have great potential for precipitating calcium carbonate within different AAS alkaline concentrations as detected utilizing spectroscopy electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD). The bacteria impact was more pronounced with the AAS of the lowest alkali dosage, around 6%, and modulus silicate of 0.8, which increased 49.6% and 150% in compressive and flexural strengths, respectively. Nevertheless, the impact was still substantial within the AAS characterization at the highest alkali dosage among the other mixes of 8% and modulus silicate of 1.2. Furthermore, the maximum healing crack width achieved was 650 µm.