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In this article is presented a differential flatness-based observer-control scheme for active nonlinear vehicle suspension systems subject to unknown exogenous disturbance excitations due to irregular road surfaces. Two active vibration controllers are proposed for hydraulic or electromagnetic suspension systems, which only require position measurements. The nonlinear effects, parameter variations, exogenous disturbances and possibly input un-modeled dynamics are lumped into an unknown bounded time-varying disturbance input signal affecting the differentially flat linear vehicle suspension system dynamics. The lumped disturbance signal and some time derivatives of the flat output are estimated by using a flat output-based linear high-gain dynamic observer. The proposed observer-control design methodology considered that the perturbation signal can be locally approximated by a family of Taylor polynomials. Some numerical simulation results are provided to show the efficiency, effectiveness and robust performance of the feedforward and feedback linearization control scheme for a nonlinear quarter-vehicle active suspension model.