In this paper, a nonlinear excitation control scheme is proposed to enhance transient stability and voltage regulation of higher-order synchronous generators. The controller is designed based on an adaptive backstepping method and the fifth-order dynamical model of synchronous generators is used to design the controller. The proposed controller is designed recursively to adapt some unknown stability sensitive parameters of synchronous generators and these unknown parameters are estimated through adaptation laws based on the formulation of control Lyapunov functions (CLFs). The proposed control scheme is also capable to overcome the over-parameterization problems of unknown parameters. Finally, the effectiveness of the proposed scheme is evaluated on a test single machine infinite bus system by applying a symmetrical three-phase short-circuit fault at different locations of the test system and compared to that of an existing adaptive backstepping controller. Simulation results demonstrate the superiority of the proposed control scheme over the existing controller in terms of settling time and providing additional damping into the system.