A hybrid sub-assembly for driving a vehicle includes at least one primary shaft, at least one secondary shaft, a transmission gearbox including at least one intermediate shaft different from the primary shaft and the secondary shaft, and an electromotive unit. The electromotive unit includes at least one reversible electric machine, and a coupling device that can take up at least one intermediate coupling position in which an output shaft of the reversible electric machine is kinematically connected to the intermediate shaft, and a secondary coupling position in which an output shaft of the reversible electric machine is kinematically connected to the secondary shaft without going via the intermediate shaft.