Later in the war, the fate of Poland came to depend on the Soviet Union, which was initially the agent of deliverance from Nazi tyranny but later was the bearer of a new form of oppression. Stalin responded to Polish indignation over the Katy Massacre by establishing an alternative Polish government of communists. The underground Polish Workers' Party (Polska Partia Robotnicza) had already been active in German-occupied Poland for over a year. In 1943 it established a small military arm, the People's Army (Armia Ludowa). The Home Army and the Polish Workers' Party acted separately throughout the war.

As the tide of war turned in favor of the Allies, the Soviet shadow over Poland and Central Europe loomed larger. When Soviet forces neared Warsaw in the summer of 1944, the Home Army, anticipating imminent Red Army assistance, launched a rebellion against the German garrisons in the capital. Instead, the Soviets halted their advance just short of Warsaw, isolating the uprising and enabling the Germans to crush it after two months of intense fighting. In retaliation against the Poles, the Germans demolished Warsaw before retreating westward, leaving 90 percent of the city in ruins.

Just before the Home Army uprising, the communist factions had formed the Polish Committee of National Liberation, later known as the Lublin Committee, as the official legal authority in liberated territory. In January 1945, the Lublin Committee became a provisional government, was recognized by the Soviet Union, and was installed in Warsaw. From that time, the Polish communists exerted primary influence on decisions about the restoration of Poland. Given this outcome, there is a strong suspicion that the Soviet failure to move on Warsaw in 1944 was an intentional strategy used by Stalin to eliminate the noncommunist resistance forces. The Red Army expelled the last German troops from Poland in March 1945, several weeks before the final Allied victory in Europe.

Data as of October 1992