This paper presents the simulation results of using a static synchronous compensator (STATCOM) to achieve damping improvement of a synchronous generator (SG)-based one-machine infinite-bus (OMIB) system with an integrated offshore wind farm (OWF) and marine-current farm (MCF). The operating performance of the studied OWF is simulated by an equivalent permanent-magnet generator (PMG) driven by an equivalent wind turbine (WT). An equivalent squirrel-cage rotor induction generator (IG) driven by an equivalent marine-current turbine (MCT) is used to simulate the operating characteristics of the MCF. A damping controller of the STATCOM is designed by using modal control theory to contribute adequate damping characteristics to the dominant modes of the studied OMIB system under various operating conditions. A time-domain scheme based on a nonlinear system model subject to three-phase short-circuit fault at the power grid is utilized to examine the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed STATCOM joined with the modal-control designed damping controller is capable of improving the stability of the studied OMIB system subject to severe disturbance.