Voltage collapse, blackout and voltage instability are considered main problems faced by the power systems which are due to the lack of reactive power in the system. One of the most important sources for injecting reactive power to the system is the flexible AC transmission systems (FACTS) devices. Thyristor-controlled series capacitor (TCSC) is one of the modern FACTS devices that can be used for reducing the overloading in line flow, allowing power system to operate in secure state and improving power system stability. In this paper, optimal steady-state load shedding and TCSC allocation in power system problems are comprehensively solved using a new robust and effective technique, called moth swarm algorithm. This algorithm is based on the moth’s orientation toward moonlight considering a new adaptive crossover and Levy flight mutation. Optimal load shedding and TCSC allocation are achieved simultaneously to remove or mitigate congestion and emergency situations. To prove the capability of the proposed algorithm for minimizing the amount of load shedding and active power loss, improving voltage profile and voltage stability, standard IEEE 30-bus test system is used under normal and contingency operations at different single- and multiobjective functions. The results obtained by the proposed algorithm are compared with those obtained by other well-known optimization techniques: TLBO, PSO, GWO, WOA, MFO. These results demonstrate the effectiveness and robustness of the proposed algorithm.