Display omitted •Decomposition mechanisms of model energetic salt, guanidium triazolate, are explored.•Decomposition pathways are electronically nonadiabatic.•CASPT2, CASMP2 and CASSCF methodologies are employed.•N2 and NH3 are predicted to be the most possible initial decomposition products. Electronically nonadiabatic decomposition pathways of guanidium triazolate are explored theoretically. Nonadiabatically coupled potential energy surfaces are explored at the complete active space self-consistent field (CASSCF) level of theory. For better estimation of energies complete active space second order perturbation theories (CASPT2 and CASMP2) are also employed. Density functional theory (DFT) with B3LYP functional and MP2 level of theory are used to explore subsequent ground state decomposition pathways. In comparison with all possible stable decomposition products (such as, N2, NH3, HNC, HCN, NH2CN and CH3NC), only NH3 (with NH2CN) and N2 are predicted to be energetically most accessible initial decomposition products. Furthermore, different conical intersections between the S1 and S0 surfaces, which are computed at the CASSCF(14,10)/6-31G(d) level of theory, are found to play an essential role in the excited state deactivation process of guanidium triazolate. This is the first report on the electronically nonadiabatic decomposition mechanisms of isolated guanidium triazolate salt.