V–Zr is a well known system where a phase transformation from rhombohedral V2Zr structure to cubic C15 Laves phase occurs during heating at about 115 K. Here we provide a thermodynamic description of this phenomenon, supported by ab initio calculations. We utilize our new method of extension of the Scientific Group Thermodata Europe (SGTE) unary thermodynamic database to zero Kelvin and demonstrate that it may be applied also to complicated intermetallic phases. To keep our analysis on equal footing with previous results for higher temperatures, data regarding a recent thermodynamic assessment of the V–Zr system (valid for temperatures above 298.15 K) were reassessed. With the help of ab initio approach, we demonstrate that the ZrV2 rhombohedral phase is not stable at 0 K and transforms to C15 Laves phase. The stability of C15 Laves phase is confirmed by analysis of elastic stability criteria and phonon spectra calculations.