<p>Phase equilibria in the ZrNi–Ni–TiNi subsystem were comprehensively investigated using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and differential thermal analysis (DTA). Both liquidus and solidus projections were constructed, and invariant equilibria involving the melt were identified and summarized. The study revealed three eutectic, two peritectic, and six transition-type invariant reactions. The formation of the ternary compound τ₃ with a BaPb₃-type crystal structure was confirmed. This phase forms via the peritectic invariant reaction L + TiNi₃ +&#xa0;Zr₂Ni₇ ⇄ τ₃ at approximately 1180&#xa0;°C, nucleates on TiNi₃ grains, and results in non-equilibrium processes. The liquidus projection contains primary crystallization fields of 11 phases, while the solidus projection comprises 11 three-phase regions formed through three eutectic, two peritectic, and six transition-type reactions. A metastable compound with about 65 at.% Ni and widely varying Ti/Zr relative amounts was observed, which promotes amorphization of eutectic melts. These results refine the description of phase equilibria in the ZrNi–Ni–TiNi subsystem and provide a reliable basis for thermodynamic modeling of multicomponent Ti–Zr–Ni alloys.</p>