The Polish Workers' Party (Polish: Polska Partia Robotnicza, PPR) was a communist party in Poland from 1942 to 1948. It was founded as a reconstitution of the Communist Party of Poland (KPP) and forcibly absorbed the Polish Socialist Party (PPS) in 1948 to form the Polish United Workers' Party (PZPR). From the end of World War II the PPR led Poland, with the Soviet Union exercising moderate influence. During the PPR years, the centers of opposition activity were largely diminished, and a socialist system was established in the country.

Arriving from the Soviet Union, a group of Polish communists was parachuted into occupied Poland in December 1941. With Joseph Stalin's permission, in January 1942 they established the Polish Workers' Party, a new communist party. The PPR established a partisan military organization Gwardia Ludowa, later renamed Armia Ludowa. In November 1943, Władysław Gomułka became secretary (chief executive) of the Central Committee of the PPR. On 1 January 1944 the party created the State National Council (KRN), proclaimed to be a wartime parliament of Poland; the body was chaired by Bolesław Bierut. In June 1944 the Union of Polish Patriots, a rival to the PPR Polish-communist organization operating in the Soviet Union, recognized the KRN as "the true representation of the Polish nation". The PPR was initially a small party with marginal support; it grew because of its alliance with the victorious Soviet Union.

In July 1944 the Polish communists, working in close cooperation with Stalin and other Soviet leaders, established and declared in liberated Lublin a provisional executive quasi-government of Poland, which they called the Polish Committee of National Liberation (PKWN). In the PKWN Manifesto issued at that time, the PKWN claimed its authority in Poland and promised post-war reconstruction as well as land reform. The KRN and the PKWN were established when the Polish government-in-exile in London was the internationally recognized government of Poland. By the end of 1944, the PKWN was replaced by the Provisional Government of the Republic of Poland, recognized by the Soviet Union, with which it signed in April 1945 a 20-year friendship, alliance and cooperation treaty. As a result of the Yalta Conference Allied determinations, the Provisional Government was converted to a formally coalition Provisional Government of National Unity (TRJN) in June 1945. The Polish government-in-exile was excluded from participation and the PPR ended up controlling the new government, which was soon recognized by the United States, the United Kingdom, and other countries. The establishment of a permanent government was conditioned on national elections being held, as mandated by the Allies. In the meantime the PPR engaged in a massive program of rebuilding the country and its industry, in combating and containing the various forms and manifestations of opposition to its rule, but also in manipulating the election preparation process to ensure the party's lasting domination.

The 1946 Polish people's referendum and the following 1947 Polish legislative election were rigged and declared a decisive victory for the PPR's "Democratic Bloc". The only legal opposition, the Polish People's Party, was marginalized. Gomułka's victory, however, was short-lived. Pressured by the Cold War, Stalin had no more patience for the Polish leader's national brand of communism, and from August 1948 the PPR was led by Bierut. In December 1948, the PPR and the purged PPS were merged to form the PZPR. What was left of democratic and pluralistic practices and pretenses was abandoned and Poland entered its period of Stalinist rule.

The Communist Party of Poland (KPP, until 1925 the Communist Workers' Party of Poland) was an organization of the far-left. The views adhered to and promulgated by its leaders (Maria Koszutska, Adolf Warski, Maksymilian Horwitz, Edward Próchniak) led to the party's difficult relationship with Joseph Stalin already in 1923–24. The Communist International (Comintern) condemned the KPP for its support for Józef Piłsudski's May Coup of 1926 (the party's "May error"). From 1933, the KPP was increasingly treated with suspicion by the Comintern. The party structures were seen as compromised due to infiltration by agents of the Polish military intelligence. Some of the party leaders, falsely accused of being such agents, were subsequently executed in the Soviet Union. In 1935 and 1936, the KPP undertook a formation of a unified worker and peasant front in Poland and was then subjected to further persecutions by the Comintern, which also arbitrarily accused the Polish communists of harboring rightist and Trotskyist elements in their ranks. The apogee of the Moscow-held prosecutions, aimed at eradicating the various "deviations" and ending usually in death sentences, took place in 1937–38, with the last executions carried out in 1940. The KPP members were persecuted and often imprisoned by the Polish Sanation regime, which turned out to likely save the lives of a number of future Polish communist leaders, including Bolesław Bierut, Władysław Gomułka, Edward Ochab, Stefan Jędrychowski and Aleksander Zawadzki. During the Great Purge, seventy members and candidate members of the party's Central Committee fled or were brought to the Soviet Union and were shot there, along with a large number of other activists (almost all prominent Polish communists were murdered or sent to labor camps). The Comintern, in reality directed by Stalin, had the party dissolved and liquidated in August 1938.

On 28 June 1940, soon after the Katyn massacre, Stalin received Wanda Wasilewska, an unofficial leader of Polish communists, at the Moscow Kremlin. The event initiated a reorientation of Soviet policies in regard to Poles. As a result, a wide range of official political, military, social, cultural, educational and other Soviet-Polish projects and activities commenced in 1940 and continued during the years that followed.

The German attack on the Soviet Union in June 1941 changed the course of World War II and with it the nature of Polish-Soviet governmental relations. Pressured by the British government, the London-based Polish government-in-exile, led by Władysław Sikorski, signed an agreement with the Soviet Union, which included a Soviet recognition of the Polish government. A Polish army was formed in the Soviet Union, but was soon taken out of there and into the Middle East by Władysław Anders. The Katyn massacre perpetrated by the Soviets on Polish POWs was revealed and the Soviet Union "suspended" diplomatic relations with the Polish government. Prime Minister Sikorski was killed in an airplane crash in July 1943. These and other factors, including disagreements about future borders, caused the Polish-Soviet relations to deteriorate.

Meanwhile, Stalin, beginning in the summer of 1941, pursued other Polish options, utilizing Polish communists and other Poles willing to cooperate, many of whom were present at that time in the Soviet Union. Polish language radio broadcasts began in August 1941; they called upon the Poles in Poland to unconditionally engage in anti-German resistance. Some prewar Polish officers were transferred to occupied Poland to conduct pro-Soviet conspiratorial activities and the Polish communists worked in November on organizing the Poles in the Soviet Union. Among the communist groups that became active in Poland after Operation Barbarossa was the Union for Liberating Struggle (Związek Walki Wyzwoleńczej), whose leaders included Marian Spychalski.