The physical and chemical behavior of carbonate minerals during subduction is key to understanding the carbon cycle process in the deep Earth. Using diamond anvil cells combined with in situ Raman spectroscopy, we investigated talc stability at 200-550 degrees C and 0.5-3 GPa, corresponding to subduction zone conditions. Results demonstrate that talc readily reacts with C-O-H fluid to form magnesite at T > 250 degrees C and P > 1 GPa, highlighting the efficient CO₂ sequestration via a stepwise carbonation process, with talc carbonation rates positively correlated with both temperature and pressure. Consequently, C-O-H fluid-driven talc carbonation effectively sequesters CO₂ from the fluid into newly formed thermodynamically more stable magnesite, implying that it has great potential for transforming talc into magnesite in the deep Earth. We have also revealed the thermodynamic conditions of the talc carbonation process and demonstrated that the stability of talc in contact with the fluid is significantly lower than that under anhydrous conditions. Furthermore, enhanced CO₂ sequestration via talc carbonation at elevated pressures and temperatures may compensate for the relatively inefficient serpentinite carbonation under the subarc. Therefore, the findings provide critical insights into the thermodynamic conditions favoring talc carbonation and contribute to a deeper understanding of carbon cycling in the Earth's interior.