A thermodynamic framework for modeling the phase equilibrium of nonferroelectric pure components and multicomponent liquid, vapor, or solid mixtures under the influence of an electrostatic field is presented. Then, this framework is used for the first time to predict the effect of this kind of field on the critical temperature and critical pressure of a multicomponent hydrocarbon mixture, giving as a result that the critical properties exhibit a downward shift with the strength of the electrostatic field applied and then a final upward shift for very huge values of the field. For these calculations an alternative mathematical expression to determine the electric susceptibilities of mixtures, and its respective compositional derivatives, is also presented; its predictive capability is illustrated by using experimental data of binary systems.