The thermal decomposition of smithsonite (ZnCO₃) was studied to obtain a universal kinetic description of the process applicable to a range of reaction conditions. A synthesized ZnCO₃ was subjected to thermoanalytical measurements under various heating and atmospheric conditions in a flow of dry N₂gas, N₂–CO₂, or N₂–H₂O mixed gases. Systematic shifts of the reaction temperature to higher and lower temperatures by the effects of CO₂ and H₂O, respectively, were identified as specific characteristics of the system. With reference to the physico-geometrical kinetic behavior of the reaction in a flow of dry N₂ gas, the retardation effect of CO₂ was demonstrated in the scheme of the physicogeometrical consecutive surface reaction (SR) and phase boundary-controlled reaction (PBR). The individual kinetics of the SR and PBR were universally described over different CO₂ pressures using an accommodation function (AF) obtained by considering the consecutive elementary steps of SR and PBR. The catalytic effect of water vapor was assumed to result from contributions of the water molecules on the consecutive elementary steps of SR and on the crystal growth of the solid product of the reaction (ZnO). An alternative AF derived considering the adsorption of water molecules on solid surfaces allowed us to obtain the universal kinetic description of the thermal decomposition over different water vapor pressures.