We report a kinetic analysis of low-temperature NiSi2-mediated crystallization of amorphous Si by in situ transmission electron microscopy. The initiation of crystallization by formation of crystalline Si on buried NiSi2 precipitates is shown to have an activation energy of 2.8±0.7 eV. Crystallization of the amorphous Si via migrating precipitates of NiSi2 occurs with an activation energy of 2.0±0.2 eV. The significance of these activation energies is discussed in terms of possible atomistic mechanisms of crystalline Si initiation and subsequent growth. Amorphous Si is reported to crystallize at temperatures as low as 450 °C.