A thermodynamic modeling of the Ni–Si–Ti system is conducted. All of the experimental phase diagram data available from the literature are critically reviewed and assessed using thermodynamic models for the Gibbs energies of individual phases. The thermodynamic parameters for five ternary compounds (τ 1 : Ti 1 Ni 1 Si 1 , τ 2 : Ti 4 Ni 4 Si 7 , τ 3 : Ti 13 Ni 40 Si 31 , τ 4 : Ti 6 Ni 16 Si 7 , and τ 5 : Ti 2 Ni 3 Si 1 ), the ternary solution phases (liquid, bcc_A2, bcc_B2, fcc_A1, and L1 2 ) as well as the binary phases (Ti 5 Si 3 , Ni 3 Si, Ni 5 Si 2 , and TiNi 3 ) showing noticeable solubilities for the third element are adjusted in the optimization. The order/disorder transitions between disordered bcc_A2 and ordered bcc_B2 phases as well as between disordered fcc_A1 and ordered L1 2 phases are treated using a two-sublattice model. The calculations indicate that the disordered and ordered phases can be described with a single equation. Comprehensive comparisons between the calculated and measured phase diagrams show that in the measured isothermal sections at 750°C, 900°C, 1000°C and 1100°C, most of the observed primary phase regions, as well as 16 out of the 26 experimentally observed invariant reaction temperatures are satisfactorily accounted for by the thermodynamic description. The liquidus projection and reaction scheme for the entire system are also presented. Further experimental work to solve a few discrepancies between calculation and experiment is emphasized.