A fuel injector having a piezoelectric actuator. A needle valve is mounted in the injector body and has an opening hydraulic surface substantially surrounded by a high-pressure fuel line in fluid communication with a high-pressure fuel chamber. A control piston partly defines a piston control chamber, which is in fluid communication with the opening hydraulic surface and the high-pressure fuel chamber. The piezoelectric actuator is activated between an off position and an on position for positioning a control valve into an open position or a closed position. A high-pressure fuel condition is maintained in the piston control chamber by fuel supplied from the high-pressure fuel chamber and independent of any actuation of the control valve. In a low pressure fuel condition, a force on the opening hydraulic surface of the needle valve member is greater than the downward force on the closing hydraulic surface thereby opening the needle valve member for producing an injection event.