This paper presents a nonlinear flatness-based control (FBC) approach for a full-order doubly fed induction generator (DFIG) in the wind turbine system. Flat outputs of the DFIG and the FBC controller are derived using differential flatness theory. The proposed approach ensures an efficient decoupled control for both active and reactive powers of the DFIG. Also, it provides a smooth trajectory tracking in the start-up and the rest to rest modes without any saturation. Therefore, the system satisfactory operates at a variable speed of the rotor with an effective active/reactive power tracking. The variable rotor speed represents a perturbation caused by changes in the wind speed or different wind energy capacity. The requirements on the active and the reactive power are converted into system variables using a high-level reference trajectory generator (HLRTG). The effectiveness of the proposed system is verified by simulations.