A fuel electro-injector for a fuel injection system for an internal combustion engine, having an atomizer equipped with a nozzle and a valve needle defining a discharge section that is annular and has a width that continuously increases as the opening stroke of the valve needle proceeds. The opening stroke is directed outwards and is caused, in a proportional manner, by the operation of an electric actuator. The electro-injector has a high-pressure environment with an annular passageway around the lateral outer surface of the valve needle to supply fuel to the discharge section, and a low-pressure environment, which communicates with a fuel outlet and is separated from the high-pressure environment by a dynamic seal between the valve needle and the nozzle. The electro-injector is provided with a hydraulic connection between the electric actuator and the valve needle, with a pressure chamber axially delimited, on one side, by the valve needle and, in use, is filled with fuel that, once compressed, axially pushes the valve needle along the opening stroke. The hydraulic connection is placed in the low-pressure environment, so that the pressure chamber only communicates with this environment.