The objective of this work is to formulate a detailed reaction mechanism of the decomposition of guanidinium 5-amino tetrazolate (GA) in the liquid phase using a combined experimental and computational approach. The experimental information comes from data published in the literature. The computational approach is based on using quantum mechanics for identifying species and determining the kinetic rates, resulting in 55 species and 85 elementary reactions. In these ab initio techniques, various levels of theory and basis sets were used. A continuum-based model for predicting species formation and mass loss of a TGA experiment was also developed and solved numerically, accounting for reversible chemical reactions and mass transfer in simulations of the GA decomposition process. The model accounts for reactions within the liquid phase and evaporation of several of the observed experimentally measured products. Simulation results for species concentrations and heat release were obtained, and these results were found to satisfactorily match the temporal experimental results previously published in literature for the decomposition of GA. Important reaction pathways in the proposed reaction scheme were identified based on a sensitivity analysis. (C) 2014 Elsevier B.V. All rights reserved.