When extracting peat for horticultural use, drainage ditches are prepared, a peatland’s vegetation is removed, and peat is harvested. These land-use changes dramatically alter the carbon, water, and energy exchanges of the peatland and convert it from a moderate sink to a large source of CO2. We adapted the CoupModel to simulate the soil CO2 emission and its associated abiotic drivers for an ongoing horticultural peat extraction site, located in Riviére-du-loup (RdL), Quebec Canada. The model outputs were first evaluated against three years (2019–2021) of manual chamber measurements of CO2 flux, and soil moisture, soil temperature profiles, and water table depth data. The model was then used to assess the sensitivity of key parameters and changes in climate forcing. CoupModel reproduced the measured soil moisture and temperature profile and showed high agreement with the water table depth and soil CO2 emissions data. Sensitivity analysis showed the importance of soil moisture availability at the soil surface on soil thermal and hydrological conditions, thus soil respiration. The simulated CO2 emission over the three evaluation years was about 168 and 151 g C m−2 y−1 when extended with seven-year of climate data. Emission factors of CO2 generated by CoupModel are lower than the default IPCC Tier 1 emission factor for peatland managed for horticultural extractions in temperate/boreal climate. Results from this modeling work can be used for IPCC Tier 3 emission reporting for the horticultural peat extraction industry, addressing land-use change issues of peatlands, and suggesting climate-smart management practices.