ABSTRACTSoil organic carbon (SOC) is a vital component of the global carbon cycle. SOC influences soil fertility and structure and is controlled by various factors, including land use, land management practices, and climate change. Biological invasion is a significant yet controversial factor that can alter SOC levels. We conducted a meta‐analysis of 445 observations from 61 published reports and followed up with field surveys to clarify the impact of plant invasion on SOC. Our results indicated that plant invasion leads to a 29% increase in microbial biomass carbon (MBC), which is one of the key fractions of SOC. Specifically, among different ecosystems, plant invasion caused MBC increases of 59% in estuaries, 59% in alluvial land, 53% in wetlands, and 80% in orchards. Furthermore, invasion by plants from the Asteraceae family resulted in a 33% increase in MBC, whereas invasion by plants from the Lythraceae family caused a 72% increase in MBC. Our field survey also revealed that plant invasion elevated the soil MBC content relative to the occurrence of native plants or bare ground. Overall, these findings suggest that plant invasion impacts soil carbon, especially by increasing MBC, which may in turn affect future invasions. These effects are influenced by the type of invasive species, ecosystem type, and soil layer depth, highlighting the complex role of biological invasion in the global carbon cycle.