Forested peatlands cover a land area of 7 X 105 km2 and store ~77 Pg C in Canada. However, the carbon (C) cycling mechanisms of temperate swamp peats have been understudied even though they contribute substantially to atmosphere-peatland C cycle. Few modelling studies have been done on temperate swamp C cycling partly because of the scarcity of field measurements in this ecosystem. These gaps create uncertainties in modeling the long-term C dynamics of temperate swamps and consequently limit our understanding of this ecosystem. To improve our understanding of the interactions and feedbacks that mediate temperate swamp C cycle, we simulated the long-term (40 years) plant processes, energy, water and C fluxes of a well-preserved swamp in Southern Ontario using a process-based model (CoupModel). CoupModel was systematically calibrated for Beverly swamp using the Generalized Likelihood Uncertainty Estimate (GLUE) method. The GLUE method reduced the uncertainty associated with multiple modelling processes linked to swamp C cycle, and reasonably improved the simulation outcome when compared to the initial local (manual) calibration. This modelling approach assisted in identifying the sensitive parameters that greatly influence temperate swamp C flux simulations and parameter interconnections that exist between simulated processes. Throughout the simulation period (1983-2023), the swamp mostly retained its net C sink status even though soil respiration increased by ~11%. However, these dynamics may be altered as we approach dangerous climate change levels. Results from this study provide valuable knowledge for predicting the fate of swamp C cycle in the region under a changing climate.