For the optimal performance of a microgrid where line resistance to reactance (R/X) ratio is high, one must consider the coupling between voltage and frequency. Furthermore, microgrid operational costs are time-varying. Thus, the voltage and frequency support controller must be flexible enough to handle technical and economic constraints. In this paper, the model predictive control (MPC) approach is proposed for voltage and frequency support considering the coupling between voltage and frequency dynamics. With the predictive model of the system, the finite horizon optimization problem is solved online and a control signal is calculated such that defined cost is minimized. By proper choice of MPC parameters, desired performance based on the availability of resources and market incentives can be achieved.