The invention relates to a method for operating a drive device (1) of a motor vehicle, said drive device (1) comprising at least one combustion engine (3) and at least one electric machine (9), as well as a dual clutch transmission (4) which can be functionally connected to the combustion engine (3) and which comprises a first sub-transmission (5), a first clutch (6) being associated therewith, and a second sub-transmission (7), a second clutch (8) and the electric machine (9) being associated therewith. In a purely electrical driving operation, the electric machine (9) is operated in a motorized manner, a driving gear is engaged in the second sub-transmission (7), and both clutches (6, 8) are disengaged. According to the invention, in order to start the combustion engine (3) during the electric driving operation, the second clutch (8) is engaged so as to drive the combustion engine (3) by means of the electric machine (9), a gear is engaged in the first sub-transmission (5), said gear having a lower gear ratio than the engaged driving gear of the second sub-transmission (7), the first clutch (6) is brought into a slip position and the second sub-transmission (7) is subsequently brought into a neutral position, the rotational speed of the electric machine (9) is increased at least to a starting rotational speed for the combustion engine (3) with the slip of the first clutch (6) being adjusted to maintain a forward torque of the motor vehicle, and the combustion engine (3) is started once its starting rotational speed has been reached. In addition, the invention relates to a device for operating a drive device of a motor vehicle.