Static Var compensator (SVC) provides reactive power support at a bus to maintaining bus voltage. When provided with a supplementary feedback controller SVC can improve system dynamic performance by damping out inter area oscillations. The conventional supplementary controller of SVC is designed by linearizing the system around an operating point. Since, it is designed at a single operating condition its performance in different operating conditions is not guaranteed. In recent years direct feedback linearization techniques (DFL) are used for designing feedback controllers. The advantage with DFL is that linearizing the system around an operating point is not required thereby making the controller independent of operating conditions. In this paper, a nonlinear supplementary controller to SVC has been proposed which utilizes DFL with prescribed degree of stability. The proposed nonlinear supplementary controller does not depend on system operating condition and is a decentralized controller. The proposed method has been implemented on 16 machines, 68 bus system representing interconnected New England Test system (NETS)-New York Power System (NYPS).