A fuel injector having an injector body and a fuel inlet communicates with a high-pressure fuel source outside the injector body and including an actuator received in a hollow chamber from which a high-pressure inlet extends to an injection valve member. Depending on the pressure in the first hydraulic chamber, fuel is injected into a combustion chamber of an internal combustion engine when the injection valve member lifts from a seat. The actuator acts directly upon a stepped piston which defines the first hydraulic chamber and actuates a control piston. The injection valve member is guided in the control piston.