The renewable energy from marine currents is highly promising as a clean, reliable and predictable energy source for the next-generation electricity generation. Therefore, the paper focuses on the design and implementation of the high-efficiency control for maximizing the marine current power generation and hence an adaptive backstepping controller with uncertainty and disturbance estimation is proposed for a generic horizontal marine turbine. The turbine design principle and dynamics modelling are presented and then the control problem is formulated. Consequently, the controller is designed to be composed of a marine turbine speed control loop and a q-axis current control loop while the uncertainty and disturbance is estimated and compensated. A swell filter is also incorporated into the control loop to smooth generator power fluctuations. The stability of the proposed control is verified via the Lyapunov synthesis and all the tracking errors are guaranteed to converge to zero asymptotically. The proposed control is verified in an experimental test bench and the test results indicate that the generator produces obviously more power (up to 30% more power) when using the proposed control in comparison with a conventional backstepping control.