In autumn 1944, due to delaying the mass production of the SU-100, the Uralmash's Design Bureau offered a project of a tank destroyer based on the SU-100. Like the SU-85M, this vehicle was the common SU-100 but armed with a 122 mm Tank Gun D-25S. Such modernisation was possible due to unified fastening of both guns.

The very first trials of the SU-122P conducted in October 1944, after that the vehicle was sent to the Governmental trials which were passed as well. By the results of both trials, the SU-122P was recommended for service, but it didn't mostly because of slow rate of fire.