In a filter cartridge (CC) for a fuel filter, the filter element (4) and the additive module are connected and typically stacked so as to allow them to be integrally inserted into a filter housing. The substantially annular filter medium (5) delimits an inner space (9) into which at least one part (24) of the attachment end of the additive module can be engaged. The liquid additive is stored in a casing forming a tank (13) that is placed at a fuel pressure and delimits an internal volume (V2) that can be varied so as to maintain an identical pressure between the liquid additive and the fuel at the periphery (V3) of the tank (13). The additive module has an external connection (28) with a liquid additive outlet pipe (12a), said external connection (28) including sealing means (37, 38) for automatically closing the outlet pipe in a fluidtight manner when the external connection is in a disengaged state.