A hybrid drive transmission unit for a vehicle with an internal combustion engine and an electric motor for the drive part, includes a power-split transmission with sub-transmissions and a torsion-damping unit with a gyrating mass interconnected between the internal combustion engine and the power-split transmission. A clutch is interconnected between the internal combustion engine and the torsion-damping unit, by which the internal combustion engine can be activated, switching from the electromotive operating mode.