Soil organic carbon (SOC) is a major sink in the global carbon budget. Recent research efforts have investigated how this store can be further increased to offset human carbon emissions as a short-term climate change mitigation strategy. However, for these strategies to be successful, the response of SOC to climate variability and change needs to be quantified. This study combines a 12-year field monitoring program with modelled outputs to evaluate SOC stability in response to climate variability in Eastern Australia over a centennial scale. Sampling of a 585 km², grazing catchment was conducted in 2006, 2014 and 2018, during drought, post-drought and drought re-entry conditions respectively. Over this period, catchment SOC was found to be stable, with mean values of 3.33% (2006), 3.20% (2014) and 3.10% (2018).  Using this field data, the BIOS2 model outputs were validated for the catchment. These outputs were then used to investigate the temporal stability of SOC under current land use conditions and the climatology of the area from 1900–2015. Mean SOC over the time series was 3.68%, while there was little variation as shown by a coefficient of variance of 0.16%. Over this period, temperature and rainfall records were found to be stable at the scale of SOC turnover times. Overall, this indicates that under consistent land use, SOC reflects only long-term climate variability. This then opens questions about how SOC will respond to expected rises in temperature in the future or the larger variability seen in paleoclimate reconstructions. These understandings are important for successful management of SOC into the future to increase soil fertility or mitigate climate change.