A turbine overspeed control system for use with a gas turbine engine of a gas turbine electrical powerplant. The overspeed control system preferably comprises a first and second overspeed control subsystem. When an overspeed condition of the gas turbine engine is detected, the first overspeed control subsystem acts to remove air from a combustion section of the engine, while the second overspeed control subsystem operates to alter the angle at which an incoming flow of air is supplied to a compressor turbine located therein. The result of operating the first and/or second overspeed control subsystem is a reduction in the speed of the gas turbine engine that is much more rapid than can be accomplished by simply shutting off a fuel supply thereto.