Researchers are always looking for ways to improve vehicle comfort and the idea of using variable stiffness and damping suspension systems has been attracting attentions. The presented research has designed, fabricated, and tested an innovative magnetorheological damper which is capable of controlling both stiffness and damping. This paper presented the detailed design and working principle of the advanced damper first and then detailed how the prototyped damper was tested by an MTS machine. The testing results verified its stiffness and damping controllable capability. Then a quarter-car model with the advanced damper was built to evaluate the performance of the damper. Sliding mode control was used to control the damper and the simulation results verified the variable stiffness and damping damper performs the best on vibration control compared with other dampers.