In this work, a nonlinear observer-based controller is designed for the attitude control of a ground vehicle with uncertainty estimation. This controller ensures the tracking of desired references in the presence of environmental disturbances and parametric uncertainties, making use of high-order sliding-mode estimators to estimate these perturbations. Furthermore, the controller incorporates a kinematic observer reconstructing the lateral vehicle velocity, based on a novel high-order sliding-mode observer. The proposed controller ensures good performance and better transient behavior with respect to existing controllers when parametric uncertainties and environmental disturbances are present. Its performance is evaluated by numerical simulation in CarSim, considering a challenging double turn maneuver, which is described in the ISO-3888 specifications.