In the present study, a powder of Ti-18Zr-15Nb biomedical alloy with spongy morphology and with more than 95% vol. of β-Ti was obtained by reducing the constituent oxides with calcium hydride. The influence of the synthesis temperature, the exposure time, and the density of the charge (TiO2+ ZrO2+ Nb2O5+ CaH2) on the mechanism and kinetics of the calcium hydride synthesis of the Ti-18Zr-15Nb β-alloy was studied. Temperature and exposure time were established as crucial parameters with the help of regression analysis. Moreover, the correlation between the homogeneity of the powder obtained and the lattice microstrain of β-Ti is shown. As a result, temperatures above 1200 °C and an exposure time longer than 12 h are required to obtain a Ti-18Zr-15Nb powder with a single β-phase structure and uniformly distributed elements. The analysis of β-phase growth kinetics revealed that the formation of β-Ti occurs due to the solid-state diffusion interaction between Ti, Nb, and Zr under the calcium hydride reduction of TiO2+ ZrO2+ Nb2O5, and the spongy morphology of reduced α-Ti is inherited by the β-phase. Thus, the results obtained provide a promising approach for manufacturing biocompatible porous implants from β-Ti alloys that are believed to be attractive candidates for biomedical applications. Moreover, the current study develops and deepens the theory and practical aspects of the metallothermic synthesis of metallic materials and can be compelling to specialists in powder metallurgy.