TiH2 has gradually gained attention in powder metallurgy because of its unique properties. This study systematically investigated the porosity, density, mechanical tensile properties, and fracture toughness of sintered samples of TiH2 as a powder metallurgy starting material. The results showed that, compared with hydrogenation-dehydrogenation titanium (HDH Ti), the density, elongation, and fracture toughness of the sintered TiH2 samples significantly improved. In addition, the contributions of grain size, porosity, and oxygen content to the yield strength of the samples are discussed, and the results revealed that a lower oxygen content and porosity are the main reasons for the differences in the mechanical properties between HDH Ti and TiH2. Finally, the experimental results are combined with first-principles calculations and simulations to construct a TiH2 phase transition model. The contribution of H atoms to the TiH2 phase transition energy barrier and activation sintering densification was investigated and elucidated, revealing the TiH2 sintering densification mechanism from the perspective of phase transition. The derived results contribute to a deeper understanding of the intrinsic mechanism of TiH2 activation sintering densification, which is highly important for the development of advanced titanium materials.