A novel nonlinear control scheme is suggested in this research for the path-following (PF) control of an underactuated autonomous underwater vehicle (AUV) in the horizontal plane. Firstly, the proper nonlinear models of the underactuated AUV with multiple uncertainties and input saturation are established. The unknown time-varying sideslip angular speed in the PF error dynamic model is treated as the kinematic uncertainty. Also, the linear superposition of parameters uncertainties, environmental perturbations, and other unmodeled dynamics is considered the lumped uncertainty. The above kinematic and lumped dynamic uncertainties are predicted by the uncertainty and disturbance estimator (UDE) approach. Such treatment is to solve the dependence on a precise mathematical model and attain a simpler controller. Secondly, an UDE-based PF controller is proposed via the backstepping frame augmented by the nonlinear tracking differentiator (NTD) and auxiliary dynamical system. The NTD is adopted to prevent the “explosion of complexity” pertinent to the standard backstepping method, and the auxiliary dynamical system is utilized to solve the issue of input saturation. Lastly, the steadiness of the entire enclosed-loop framework is presented. Conducting comprehensive simulations are presented to assess the efficacy and robustness of the devised controlling scheme.