The 12th Army was formed on October 3, 1918, in the region of Astrakhan and the Eastern part of the Northern Caucasus.
It fought in Ukraine against Anton Denikin's Volunteer Army, and then against the troops of Symon Petliura, which it pushed back behind the Zbrucz River.
On December 10, it fought in the 6-day long 4th Battle of Kiev to retake the city from the White Army.
In the spring of 1920, as part of the Southwestern Front, the 12th Army was deployed against the Polish offensive in Ukraine and was pushed back over the Dnieper.
At the end of the Polish-Soviet War, the 12th Army had suffered heavy losses and was disbanded on December 25, 1920.