This study examines how microbial carbon use efficiency (CUE) influences soil organic carbon (SOC) formation and persistence using global datasets, modeling, and meta-analysis. Findings reveal that CUE is four times more crucial than factors like carbon input or decomposition in determining SOC storage and its global distribution. A positive correlation between CUE and SOC content highlights microbial CUE as a key factor in SOC storage, crucial for predicting SOC feedback to climate change.