A unified secondary controller based on finite control set-model predictive controller (FCS-MPC) approach is proposed for frequency control and voltage restoration of islanded-based AC Microgrid. The considered microgrid system consists of two distributed generation (DG) units with parallel inverters connected to photovoltaic (PV) and battery energy storage systems. The errors generated by the droop controller are eliminated using a secondary controller, which introduces corrective offsets to restore frequency and voltage to their nominal values. Unlike conventional approaches that employ traditional MPC and PI-based secondary control, the proposed method utilizes FCS-MPC in both primary and secondary control layers, establishing a unified predictive framework. An FCS-MPC is also used to control the bidirectional DC-DC converter and PV boost converter to ensure a stable DC-link voltage. A delay-compensated multi-step prediction mechanism is incorporated in the primary control layer to mitigate the effects of computational delays. The effectiveness of the proposed control strategy is investigated under load disturbances and delay conditions. Furthermore, the performance is compared with a traditional MPC and PI-based secondary controller using the OPAL-RT OP4510 platform, demonstrating enhanced dynamic response and robustness.