A Fixed-Switching-Frequency Model Predictive Control (FSF-MPC) for Master-Slave inverters in microgrids is proposed in this paper. The Master is a three-phase, two-level inverter with an LC filter, while the Slave is a three-phase, two-level inverter with an LCL filter. The inverters are connected in parallel in a microgrid, composed of different loads. The voltage and current inner control loops of the Master-Slave FSF-MPC are presented for both inverters. Then, two modes of operation are proposed: grid-connected and islanded, and the primary control for both cases is developed. Finally, Hardware-in-the-Loop (HIL) results are presented for different operational conditions of the microgrid with load-related disturbances. The HIL results validate the good performance of the proposed Master-Slave FSF-MPC, including fast dynamic response, multi-objective control, and fixed switching frequency.