Throughout its existence, the Soviet Union was a one-party state dominated by the Communist Party of the Soviet Union. From 1936, this dominance was formalised under the country's constitution (commonly known as the Stalin Constitution), which established the leading role of the party.

In addition to the central party apparatus (referred to as the "all-Union", or branch of the party), 18 nonconcurrent republic-level branches also existed with autonomous leadership. At the outset, many republic-level parties differed in ideology from the all-Union party, including anti-colonial activists, national communists and Islamic modernists. While these factions were largely destroyed in the Great Purge, republic-level parties maintained different factions and at times different ideologies from their all-Union counterpart.

As part of Mikhail Gorbachev's policies of perestroika, the dominance of the CPSU in politics was gradually diminished through a process of granting further powers to soviets and eventually by the abolition of the leading role of the party. From 1988, various political parties were established, primarily advocating for the autonomy or independence of the republics and increased rights for ethnic minorities.

Ruling party The Soviet Union was dominated by the Communist Party of the Soviet Union from its foundation; while the Communist Party was originally intended by Vladimir Lenin, leader of the party and first Premier of the Soviet Union, to play a limited role in administration, it increasingly intertwined itself with the bureaucracy of the former Russian Empire and later the Soviet Union. A desire to prevent subversion of party policy by potentially disloyal bureaucrats motivated increased infiltration of the state apparatus by party functionaries, with the usage of state resources to expand the party's presence in rural areas where popular support was nonexistent and in cases where the party's resources were limited. Over time, particularly during Joseph Stalin's rise to power, party officials utilised the ambiguous relation between the party and the bureaucracy to their benefit, and the Soviet Union became a de facto one-party state. The position of the CPSU as the sole ruling party of the Soviet Union was established by the 1936 Constitution of the Soviet Union (commonly known as the Stalin Constitution due to its adoption under the leadership of Joseph Stalin).

With the advent of Mikhail Gorbachev's campaigns of perestroika and glasnost, the leading role of the party and the intersection of party and state positions was gradually dismantled. New state governing organs were established separately from the party (the Congress of People's Deputies and the presidency). Attempts to completely abolish the leading role of the party were originally met with strong opposition from Gorbachev; however, with pressure on the party increasing from the Revolutions of 1989 and the Singing Revolution in the Baltic republics, the republics gradually began abolishing the leading role of the party. These changes increasingly pressured the central party apparatus, in turn, and in February 1990, Gorbachev acquiesced to abolishing the party's supremacy over the state, leading to the establishment of a multi-party system.

The Communist Party of the Soviet Union had autonomous divisions in all republics of the Soviet Union apart from the Russian SFSR. In terms of party organisation, all republic-level parties replicated the structure of the all-Union () party, with the exception of the position of second secretary. The second secretary traditionally served as the all-Union party apparatus's plenipotentiary to the republic, influencing the party's organisation and policies. + All-Union and republic-level communist parties in the Soviet Union, 1921–1991 Republic Established Dissolved Remarks All-Union 1912 1991 Armenia 1920 Azerbaijan 1920 Originally a breakaway from the Muslim Social Democratic Party. During the Anglo-Soviet invasion of Iran and the Iran crisis of 1946, the party exerted influence over Soviet-occupied territories, attempting to secure the annexation of Iranian Azerbaijan into the Azerbaijani SSR. Beginning in the 1960s, the party was increasingly dominated by patronage clans, typically favouring migrants from western regions of Azerbaijan. From 1969, the party was controlled by Heydar Aliyev, who served as the party's First Secretary and later as a member of the all-Union Politburo until being forced to retire by Gorbachev in 1987. BukharaRuling party of a legally independent state de facto part of the Soviet Union. 1918 1924 Formed by radical followers of the Jadid movement in the Emirate of Bukhara; overthrew the emirate in 1920. Included the poor as well as members of the clergy and the bourgeois. The party's leadership sought to establish an independent Bukharan nation-state, pursue Islamic modernist policies and develop the economy through state control. While the Uzbek SSR was explicitly the legal heir to Bukhara under Soviet law, the Jadid-aligned members of the party were removed from power. Byelorussia 1917 2023 Formed from a split in the Belarusian Socialist Assembly. In its early years, the party was primarily concerned with Bundism factions, with the Bundists being purged as the most significant dissenting faction within the party. Between 1956 and 1980 the party was largely controlled by former Soviet partisans, who oversaw rapid economic development and industrialisation at the same time as Russification. The 1986 Chernobyl disaster, the reveal of the 1937 mass execution of Belarusians and a growth in support for preserving the Belarusian language ultimately resulted in a collapse in support for the party. Through delaying reforms, the party's elites remained in power until 1994. Estonia 1920 1990 Originally organised as a Leningrad-based subversive group against the Estonian government, with ties to trade unions and leftist members of the Estonian military. The party was banned after a 1924 coup attempt, and most of its underground members fled to the Soviet Union, where they were executed in the Great Purge. During perestroika, the party was divided between hardline Stalinists who sought to preserve the Soviet Union (largely backed by ethnic Russian settlers) and moderate supporters of perestroika, who were generally ethnic Estonians and supported Estonian membership in a Soviet confederation. The former group established the Intermovement in 1988. Georgia 1921 1991Banned. Established after the Soviet invasion of Georgia. Initially was involved in the Georgian affair, a dispute in which the party's leadership sought to preserve Georgian autonomy within the Soviet Union. The party was sidelined in 1929 by Stalin, with the justification that its leadership consisted of "nationalist deviationists". From 1953, the party was led by Vasil Mzhavanadze, a supporter of Nikita Khrushchev; Mzhavanadze's rule was marked by widespread corruption, leading to his replacement by Eduard Shevardnadze in 1972. The party was removed from power following the Massacre of Tbilisi; it was banned in 1991 by Zviad Gamsakhurdia after the failure of the coup attempt. Karelo-Finland 1940 1956 Kazakhstan 1936 1991 Originally dominated by European settler-colonists, the party made widespread attempts to encourage Kazakhs to join the party, including mullahs and beys; as Kazakh membership increased party organisation became increasingly stratified along ethnic lines. Over time, party membership became dominated by members of the , with the First Secretary traditionally being a Kazakh of the senior jüz. Khorezm 1920 1924 Kirghizia 1925 1991 Initially marked by disputes over wealth redistribution and whether European concepts of class were applicable to Kyrgyz society; supporters of retaining a pastoralist economy and those expressing the idea that the Kyrgyz were inherently democratic (led by ) were executed during the Great Purge. The party was defined by rivalries between regional and tribal patronage clans. Latvia 1904 1991 Lithuania 1918 1991 Moldavia 1940 1991 Members of the Romanian Communist Party were largely barred from membership due to concerns about their loyalty to the Soviet Union, and membership remained dominated by Russians and Ukrainians. Ethnic Romanians were excluded from politics with the exception of Ivan Bodiul, and elites engaged in wide-reaching corruption. Legally succeeded by the Agrarian Party of Moldova; the Party of Communists of the Republic of Moldova also claims descent from the party. Tajikistan 1924 Initially dominated by national communists and Jadids, most of whom were executed during the Great Purge. Following World War II, the party was dominated by a patronage clan from Leninabad which, unlike other Soviet patronage clans, developed into a familial clan through marriages. They formulated an alliance with the southern Kulobi people against the Pamiri people and the Qurghonteppa Oblast. Attempted marketisation led by the party from 1985 was disastrous, and both patronage and economic failures contributed to the Tajikistani Civil War. Turkestan 1918 1924 Originally dominated by members of the ethnically Russian former colonial elite of Russian Turkestan. Unable to successfully mount an opposition movement to Russian hegemony, most intellectuals joined the party and some Jadids obtained leading positions, enabling Jadid-inspired reforms. Turkmenistan 1924 1991 Formed from Turkmen sections of the communist parties of Khorezm, Turkestan and Bukhara. While Turkmen cadres initially were formally placed in leading positions, real power was dominated by Europeans, who were given positions as "dual secretaries" at all levels of bureaucracy and reported to Moscow. Given the lack of a Turkmen proletariat, the party's support base was the peasantry, with theoretical class structures based on those of Russia. Tribalism remained a significant issue throughout the party's existence, and from the 1970s, the Teke tribe dominated the party. Reformed into the Democratic Party of Turkmenistan in 1991. Ukraine 1918 1991 Established by a series of splits in the Ukrainian Socialist-Revolutionary Party. The party was initially dominated by ideological splits between national communists (generally hailing from the central Dnieper Ukraine), who favoured increased autonomy, and those from southern and eastern Ukraine, who argued that the Ukrainian party's role was to implement the all-Union party's directives. The national communists were killed during the Great Purge.

Beginning in the mid-1960s, the party increasingly became dominated by regional patronage clans. Under Petro Shelest (r. 1963–1972), national communism was again pursued before Volodymyr Shcherbytsky abandoned the policy. During the 1989–1991 Ukrainian revolution the party was split between hardliners led by Stanislav Hurenko and national communists led by Leonid Kravchuk.

Several parties claimed to succeed the Communist Party of Ukraine, including the Communist Party, the Socialist Party and the Party of Democratic Revival of Ukraine. Uzbekistan 1925 1991 Established out of the Bukharan and Turkestani communist parties; originally included Jadid sympathisers and anti-colonial activists. Elites from Samarkand and Tashkent dominated the party. Several high-ranking figures were implicated in a wide-reaching corruption scandal during the 1980s and either arrested or died; whether the arrests were motivated by genuine anti-corruption efforts or a desire to crush Uzbek nationalism remains unclear.

Factions Left Opposition (1923–1933) Workers' Truth (1921–1923) Workers' Group (1923–1930) Right Opposition (1924–1933) United Opposition (1926–1927) Left-Right Bloc (1930) Union of Marxist-Leninists (1932) Bloc of Soviet Oppositions (1932–1933) Anti-Party Group (1957) Soyuz (1990–1991) Bolshevik Platform (1991) State Committee on the State of Emergency (1991)

Underground True Communists (1940)