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Biological control is described as the suppression of one or more populations of plant pathogens using introduced or resident living species rather than disease-resistant host plants. This can be accomplished by the use of microbial biological control agents (MBCAs) where they biologically control plant pathogens interacting with their hosts via a range of modes of action. Overuse of pesticides has had a negative impact on the climate in recent decades that gave rise to human health issues. This posed a dire need to explore alternative strategies that are comparatively safe, environmental, and monetarily feasible. The employment of MBCAs is found to be a highly effective way to regulate several diseases of the exiting flora caused mainly by nematode infestation and bacterial or fungal pathogens. Microbial inoculants suppress a particular form of plant disease or regulate soils so that plant-associated species and native soil can work together to suppress the disease. Microbes, such as bacteria, protozoa, algae, and fungi, frequently interact with plants in several ways including protocooperation, mutualism, commensalism, rivalry, neutralism, amensalism, predation, and parasitism. These interactions are cascades of highly regulated metabolic events that combine various kinds of action. Compounds such as enzymes, signaling compounds, and other interfering metabolites are released in situ at low levels during the interaction. Pseudomonas, Erwinia, Bacillus, Agrobacterium, Rahnella, Lysobacter, Myxobacteria, Enterobacter, and Streptomyces are some of the bacterial genera that have major biocontrol potential to mitigate crop plant diseases. Several species, including P. fluorescens, P. putida, P. cepacia, P. aureofaciens, P. tolaasii, P. fluorescens (strains A1, BK1, TL3B1, A506, and B10), Erwinia herbicola, B. cereus (strain UW85), Agrobacterium radiobacter (strain K84), Rahnella aquatilis have been proved beneficial against various crop diseases. Likewise, Trichoderma harzianum, Glomus fasciculatum, G. macrocarpum, and Pisolithus tinctorius are known to induce plant defense response against phytotoxic effects caused by different pathogenic strains. This review highlights the role of MBCAs against pathogenic microorganisms and their mode of action in terms of the ability to enhance plant defense systems for their improved growth. [ABSTRACT FROM AUTHOR]