The present invention relates to a powertrain for a hybrid type vehicle with a thermal engine (10), notably of internal-combustion type, an electric machine (12) connected to an axle shaft (24) of the vehicle and a transmission device (36) comprising a primary transmission shaft (38) connected to drive shaft (18) of thermal engine (10) through a disengageable coupling (44) and carrying at least two first gear wheels (56, 58) cooperating with at least two second gear wheels (60, 62) carried by a secondary transmission shaft (40) connected to the axle shaft. According to the invention, primary transmission shaft (36) is connected to an auxiliary electric machine (14).