This paper provides a consistent thermodynamic data set for the whole Al-Nb-Ni ternary system via thermodynamic modeling. The order/disorder transitions between disordered bcc_A2 and ordered bcc_B2 phases as well as between disordered fcc-A1 and ordered L12 phases are treated using a two-sublattice model. The calculations indicate that the disordered and ordered phases can be described with a single equation. 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. Inconsistent experimental information is identified and ruled out. Optimal thermodynamic parameters are then obtained by considering reliable literature data. Comprehensive comparisons between the calculated and measured phase diagrams show that almost all the accurate experimental information is satisfactorily accounted for by the present thermodynamic description.