In this work, the thermal decomposition kinetics of howlite were investigated at different heating rates by using Coats–Redfern, Ozawa, and Kissinger–Akahira–Sunose kinetic models under non-isothermal conditions. The thermal decomposition of howlite occurred in two dehydroxylation stages. Results indicated that it decomposes in the first dehydroxylation stage at a very slow rate due to the higher thermal stability of the mineral. Kinetic parameters were determined using the above-mentioned models for all decomposition stages. The activation energies calculated from the Ozawa and Kissinger–Akahira–Sunose isoconversional methods fit well with each other, while the activation energies calculated with the Coats–Redfern method were different. It was also seen that the activation energy of the decomposition reaction changed with the degree of conversion, suggesting that the reaction mechanism is not single-step.