This meta-analysis examines the stability and decomposition of biochar in soil, focusing on its mean residence time (MRT) and priming effects. Using 128 observations from 24 studies with stable and radioactive carbon isotopes, the study found that the decomposed amount of biochar increased logarithmically with experimental duration, while the decomposition rate decreased over time. The MRTs of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years, respectively, indicating that only a small part of biochar is bioavailable, with the remaining 97% contributing to long-term carbon sequestration. The priming effect, evaluated using 116 observations from 21 studies, showed a slight negative impact on soil organic matter (SOM) mineralization, with significant negative priming observed in studies lasting less than half a year, for crop-derived biochar, fast pyrolysis, low pyrolysis temperatures, and small application amounts. In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. The study concludes that biochar can persist in soils for centennial scales and has a positive effect on SOM dynamics and carbon sequestration.This meta-analysis examines the stability and decomposition of biochar in soil, focusing on its mean residence time (MRT) and priming effects. Using 128 observations from 24 studies with stable and radioactive carbon isotopes, the study found that the decomposed amount of biochar increased logarithmically with experimental duration, while the decomposition rate decreased over time. The MRTs of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years, respectively, indicating that only a small part of biochar is bioavailable, with the remaining 97% contributing to long-term carbon sequestration. The priming effect, evaluated using 116 observations from 21 studies, showed a slight negative impact on soil organic matter (SOM) mineralization, with significant negative priming observed in studies lasting less than half a year, for crop-derived biochar, fast pyrolysis, low pyrolysis temperatures, and small application amounts. In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. The study concludes that biochar can persist in soils for centennial scales and has a positive effect on SOM dynamics and carbon sequestration.