Methyltrichlorosilane (MTS) is a precursor commonly used in the production of silicon carbide for composites, protective coatings, and structural ceramics. Experiments suggest that MTS decomposes in the gas phase to produce a large number of species whose surface reactivity is expected to vary widely. In this work, we discuss the development of a gas-phase mechanism that describes the decomposition of MTS. Rate coefficients for the reactions were obtained from literature sources, theoretical methods, and comparisons with analogous reaction chemistry. Several unknown reaction rates were fit to experimental measurements of MTS decomposition. The results are used to predict the major reaction paths, identify reactions to which product concentrations are sensitive, and determine the rate-limiting step for MTS decomposition.