Microbial inoculants are microorganisms including bacteria and fungi that are isolated from their natural habitats, cultured under controlled conditions, and applied to plants or soils to promote specific beneficial outcomes. These biological agents have emerged as an effective agrotechnical approach to benefit sustainable farming practices. Despite the growing number of studies on plant growth-promoting rhizobacteria (PGPR) and fungi (PGPF), a comprehensive synthesis quantifying their global effects and examining moderating factors remains lacking. Existing literature predominantly examines specific regions, crops, or microbial taxa, limiting our general understanding of how inoculant perform under diverse agroecological conditions. To fill this gap, we conducted a systematic review that integrated (i) mapping of research trends in PGPR and PGPF studies and (ii) quantitative synthesis of experimental evidence from 280 published reports across 68 countries. The analysis evaluated the overall impact of microbial on plant performance, soil enzyme activities, and nutrient uptake, while identifying the key moderators influencing these outcomes. Our results showed that most studies were carried out in greenhouse and lab conditions with India, China, Pakistan, Iran and Turkey leading in publication volume (148; 57.1%). Over 90% of the articles processed were indexed by Scopus and/or Web of Science databases. The efficacy microbial inoculants was context-dependent. For example, positive responses to inoculation were more pronounced in herbaceous plants than in shrubs and trees. The efficacy and benefits also varied according to the type of inoculant and the functional group of the host plant.