Mangrove ecosystems are dynamic coastal environments that offer essential ecological services, socioeconomic benefits, and resilience against climate change. Central to their functionality there are complex microbial communities—primarily bacteria and fungi—that drive key biogeochemical processes such as organic matter decomposition, nitrogen fixation, carbon sequestration, and sulfur cycling. This review aims to synthesize current knowledge on mangrove microbiomes, focusing on microbial taxonomic diversity, ecological roles, and environmental responsiveness. The effect of abiotic factors such as salinity, tidal regimes, vegetation type, and anthropogenic pressures on microbial community structure and function is also assessed. Key findings highlight the presence of both conserved microbial taxa across biogeographic regions and functional adaptations to local conditions, underscoring the global ecological significance of these microbial assemblages. Particular attention is given to microbe-mediated nutrient cycling, symbiotic plant–microbe interactions, and microbial contributions to pollutant degradation, including microplastics and heavy metals. Additionally, recent advances in omics-based approaches have expanded our understanding of microbial functionality and unveiled promising avenues for biotechnological applications, such as enzyme production and bioactive compound discovery. The review also identifies critical knowledge gaps, including the need for long-term monitoring, methodological standardization, and integrated multi-omics frameworks. Overall, recognizing microbial communities as foundational components of mangrove health is essential for effective conservation, ecosystem restoration, and sustainable resource management in the face of accelerating global environmental change.