A reliable Calphad-based database has been developed for multi-principal element alloys with Al, C, Co, Cr, Fe, Mn, Ni, and V components. For this purpose, the Ni–V binary system and the Al–Co–Mn, and Al–Co–Fe ternary systems were assessed using experimental data from the literature. In addition, ab initio calculations for Ni–V at 0 K for all experimentally reported stable phases were performed to enhance the thermodynamic modeling of this system. The main focus in modeling of the ternary systems was to handle order–disorder (bcc/B2) transition, which is dominant over a wide range of compositions and temperatures. In the Al–Co–Fe system, apart from the bcc/B2 transition, there was also magnetic transitions in the bcc and B2 phases. Therefore, a four-step procedure was used to reasonably model this system. Following construction of the database, several Calphad calculations were carried out. The results were compared with experimental data to validate the reliability of the database. Finally, the constructed database was used to predict alloys and facilitate experimental alloy design with promising results.