The present invention is for an apparatus and method for an actuator using an magnetohydrodynamic (MHD) pump to electrically generate a hydraulic pressure and a flow in a liquid metal, thereby causing the liquid metal to act on and extend an expansion member such as extend bellows, membrane, rolling diaphragm, or a piston in a cylinder. The resulting mechanical displacement of the expansion member may be beneficially used to exert a force, pressure, and/or to move elements of a machine. In particular, mechanical displacement (stroke) of the actuator may actuate elements of a humanoid robot, or artificial limb prosthetic, or flight control surfaces of an aircraft. The actuator may be arranged to operate bi-directionally by reversing the polarity of the electric current supplied to the MHD pump. Force exerted by the MHD actuator may be controlled by varying the electric current of the MHD pump drive current.