The analysis and design of a novel active suspension system incorporating a negative stiffness spring are investigated in this paper. The suspension structure consists of the mechanism that employs a combination of ordinary and negative stiffness springs and damping element. The resulting system yields superior performance in terms of mobility, maneuverability, and stability, particularly in harsh terrains and/or off-road environment. However, its dynamics are highly nonlinear and cannot be handled directly by conventional design techniques and methodologies. In this paper, the formulation of the proposed active suspension system consists of two phases: analysis and synthesis. In the analysis phase, nonlinear controls based on the advanced feedback linearization methodologies of the differential geometric theory is considered. The approach renders the difficult task of developing nonlinear controls rather simple. In the synthesis phase, which is required for real-world implementation and mechanization, observer-based controls are conducted. Extensive simulation studies show that the system can effectively reject all the harsh road disturbances while stabilizing the vehicle platform remarkably well. Hence, not only the specific active suspension system can increase the vehicle mobility and maneuverability, provide a stable platform for weapon firings and improved target hit probabilities, but it can also lower the power consumption of the vehicle, reduce the absorbed power by the driver, and improve the overall fuel economy of the vehicle.