Ultrafast relaxation dynamics of excess electrons were investigated in cesium-doped cesium iodide melt at various temperatures. It is shown that the excess electrons are predominantly polarons in agreement with earlier conclusions from steady-state absorption studies that with increasing cation size, the tendency of formation of bipolarons decreases. Furthermore, temperature-dependent measurements show that ionic diffusion is an important process which determines the relaxation dynamics of excess electrons in M–MX solutions. The activation energy obtained from the temperature dependent relaxation rates of excess electrons agrees well with those calculated from ionic self-diffusion coefficients. This is a further confirmation of our earlier conclusions that the activation energy involved in the relaxation process is nothing but the energy required to form a hole. We have further shown that the relaxation rates of excess electrons in alkali-metal-doped alkali halide melts serve to estimate the size of polarons. Finally, the nature of the relaxation dynamics of polarons is shown to be independent of the excitation region within the stationary absorption spectrum of excess electrons. This is in contrast to the observations of hydrated electrons in aqueous solutions and adds further support to the thermodynamic defect model proposed to explain the electrical and optical properties of excess electrons in molten alkali-metal-doped alkali halide mixtures.