When the Red Army managed to break the Leningrad blocade in January 1943 south of Lake Ladoga, the new German Tiger tank, prematurely put into action, fell into their hands.
Instant tests however rendered severe deficencies obvious as none of the existing 76mm tank guns, neither the F-34 of the T-34 nor the ZiS-5 of the KV, were able to penetrate the Tiger's frontal armour but within the shortest range.

As a consequence, the Soviet Defence Committee (GKO) ordered the development of a tank capable of dealing with the upcoming fascist menace.
As a stopgap, the GKO ordered the installation of the 52-K 85mm AA gun into the hull of the SU-122, already in production at the Uralsky Heavy Machinery Plant im. Sergo Ordzhonikidze (»UZTM«).
However, the gun proved to be too large for the hull without modification, so Grabin's Central Artillery Design Bureau (TsAKB) had to develop an appropriate gun, the S-18 gun.

At the same time, F.F.Petrov's design bureau at Plant #9 started an own gun development, resulting in the D-5S-85 which outclassed the Grabin design during all subsequent tests.

So the new SU-85 was accepted for production on August 7, 1943, with just 20 percent new components, but 73% borrowed from the tank T -34 and 7% from the SU-122.
The first 150 machines were finished at UZTM (»Uralmash«) still in August with another 750 during the rest of the year, just in time to participate at the Dnyepr crossing and the liberation of Kiev with the new tank destroyer battalions.

In action, the new tank proved rather successful, although it had to approach the Tigers and Ferdinands up to 500 m to be effective and was hindered by the lack of any close fight protection.

With the arrival of the T-34/85 and the more powerful SU-100 in the fall of 1944, the SU-85 finally became obsolete, although the last 315 of the 2600 totally produced achieved the new uparmoured SU-100 hulls as so-called SU-85M(odernized).