An endothermic/electric hybrid propulsion system for a vehicle, comprising: - a first propulsion unit, of the electrical type, provided with at least a first electric machine coupled to a transmission shaft, in which said transmission shaft is coupled to a differential of said vehicle; - a second propulsion unit, of the hybrid type, provided with an output shaft and comprising at least one internal combustion engine and at least a second electric machine which is configured to be selectively coupled together to provide torque to said output shaft in an independent or combined manner; - a coupling member operatively interposed between the output shaft of the second propulsion unit and the transmission shaft of the first propulsion unit, wherein said coupling member is configured to be selectively switched between an engagement condition in which it couples said first and said second propulsion unit, and a disengagement condition, in which it disengages the second propulsion unit from the first propulsion unit, wherein the second propulsion unit comprises a transmission device operatively interposed between the internal combustion engine, the output shaft and the second electric machine the system being characterized in that the trnsmission device has at least a first operating condition in which it allows the transmission of torque between the second electric machine and the internal combustion engine through said output shaft; said transmission device comprising a plurality of gearsets (12, 13, 14) defining a corresponding plurality of transmission ratios between an input shaft and said output shaft of the second propulsion unit, wherein said internal combustion engine is coupled to said input shaft. - a first propulsion unit, of the electrical type, provided with at least a first electric machine coupled to a transmission shaft, in which said transmission shaft is coupled to a differential of said vehicle; - a second propulsion unit, of the hybrid type, provided with an output shaft and comprising at least one internal combustion engine and at least a second electric machine which is configured to be selectively coupled together to provide torque to said output shaft in an independent or combined manner; - a coupling member operatively interposed between the output shaft of the second propulsion unit and the transmission shaft of the first propulsion unit, wherein said coupling member is configured to be selectively switched between an engagement condition in which it couples said first and said second propulsion unit, and a disengagement condition, in which it disengages the second propulsion unit from the first propulsion unit, wherein the second propulsion unit comprises a transmission device operatively interposed between the internal combustion engine, the output shaft and the second electric machine the system being characterized in that the trnsmission device has at least a first operating condition in which it allows the transmission of torque between the second electric machine and the internal combustion engine through said output shaft; said transmission device comprising a plurality of gearsets (12, 13, 14) defining a corresponding plurality of transmission ratios between an input shaft and said output shaft of the second propulsion unit, wherein said internal combustion engine is coupled to said input shaft.