The leading role of the party is a constitutional principle most common in communist states. It holds that the ruling party leads the state by virtue of being the vanguard of the proletariat.
The leading role of the party was first enshrined in Article 126 of the Stalin Constitution, which described the Soviet Communist Party as "the vanguard of the working people in their struggle to strengthen and develop the socialist system and is the leading core of all organizations of the working people, both public and state."
The text of the article follows in English translation.
The leading and guiding force of the Soviet society and the nucleus of its political system, of all state organisations and public organisations, is the Communist Party of the Soviet Union. The CPSU exists for the people and serves the people.
The Communist Party, armed with Marxism–Leninism, determines the general perspectives of the development of society and the course of the home and foreign policy of the USSR, directs the great constructive work of the Soviet people, and imparts a planned, systematic and theoretically substantiated character to their struggle for the victory of communism.
All party organisations shall function within the framework of the Constitution of the USSR.
Similar provisions were found in the constitutions of other Communist states. It was used to justify bans on opposition parties, as well as harsh measures against opposition of any sort. The theory was that since the party was the vanguard of the proletariat, its right to rule could not be legitimately questioned. When non-communist parties were allowed, they were forced into permanent coalitions with the communists. Non-communist parties in these systems were largely subservient to the Communist Party and had to accept its leading role as a condition of their continued existence.
The Communist Party of the Soviet Union, other political parties as well as labor, youth and other public organisations and mass movements, through their representatives elected to the Councils of People's Deputies and in other forms participate in the policy-making of the Soviet state, in the management of state and public affairs.