Earthworms are important ecological engineers, and they enhance sustainable agriculture via soil–ecosystem interactions. Earthworms flourish in microbe-abundant habitats by utilizing innate defense systems and antibacterial peptides to thwart microbial threats. Processed organic matter, or vermicast (more popularly referred to as worm cast), is a highly nutritious soil amendment that can increase soil productivity and maintain the multitude of lichens and bacteria that are necessary for plant nutrition and soil fertility. The earthworm gut is a dynamic bioreactor housing a highly diverse microbial community that is engaged in organic matter decomposition and nutrient mineralization, as well as pollutant transformation processes. Soil microbial communities perform essential functions, such as carbon sequestration, nitrogen fixation, and denitrification, in regulating the gut microbiota. Moreover, earthworms enhance soil aggregation, which helps retain water, reduces erosion, and promotes nutrient stabilization, increasing ecosystem resilience over the long term. Earthworms and their microbiota findings highlight the potential for sustainable agriculture, which could replace chemical fertilizers and pesticides. In addition, earthworm casts and intestines have also been shown to harbor microbial diversity with functional groups capable of producing phytohormones, siderophores, and biopesticides to increase plant growth as well as pathogen suppression. The earthworm and its associated microbes combine both conventional and high-tech agricultural practices, thus providing a sustainable, efficient, and earth-friendly agricultural system. This chapter describes the noncapitalized niches of earthworms and their idealism to create mutualistic relevance to sustainable agricultural enhancement practices.