This paper deals with the current and speed control of a Doubly-Fed Induction Generator (DFIG)-based marine tidal current applications. DFIG has been already considered for similar applications, particularly wind turbine systems using mainly Integer-Order PI (IOPI) controller. However, such kinds of controllers do not adequately handle DFIG parameter variations under the harsh marine environment and decrease the system performances. As a result, to increase the generated power and the efficiency of the system, Fractional-Order PI (FOPI) controller, which is developed from the conventional IOPI controller and fractional calculus theory, is proposed in this paper. This FOPI controller has the outstanding advantages in terms of stability, robustness and dynamic performance. The proposed control strategy is inserted into a global simulation tool that accounts for the resource and the marine turbine models. The simulation comparisons between IOPI and FOPI controllers are presented and analyzed.