He was born in Verkhneye, Yekaterinoslav province, of the then Russian Empire. He joined the Bolshevik party in 1903. Following the Revolution he was a member of the Ukrainian provisional government and Commissar for internal affairs. Organizing the defense of Tsaritsyn during the civil war, he became closely associated with Joseph Stalin.
Voroshilov was elected to the Central Committee (1921-1961). In 1925 after the death of Mikhail Frunze, Voroshilov was appointed People's Commissar for military and navy affairs and chairman of the Military Revolutionary Council of the USSR, a post he held until 1934. He was made full member of the newly formed Politburo in 1926, remaining a member until 1952. He was heavily involved in the Great Purge that lasted throughout the 1930s.
Voroshilov was appointed People's Commissar for Defence in 1934 and a marshal of the Soviet Union in 1935. He lost his post as defense commissar over the Russo-Finnish war (1939-1940). During World War II, Voroshilov was a member of the State Defense Committee . He was made commander of the northwest armies for two months in 1941, but failed to prevent the Germans from surrounding Leningrad and promptly lost that office. In 1945-47 he supervised the establishment of the communist regime in Hungary.
In 1952, Voroshilov was appointed a member of the party Presidium of the Supreme Soviet. Stalin's death prompted major changes in the Soviet leadership and in March 1953, Voroshilov was approved as chairman of the Presidium with Nikita Khrushchev as General Secretary. Voroshilov, Georgy Malenkov and Khrushchev brought about the arrest of Lavrenty Beria (1953). Following disagreements with Khrushchev he temporarily joined the conservatives Malenkov, Kaganovich and Molotov, in an unsuccessful attempt to remove Khrushchev from power in June 1957, but he soon switched sides and supported Khrushchev.
On May 7, 1960, the session of the Supreme Soviet granted Voroshilov's 'request' for retirement and elected Leonid Brezhnev chairman of the Presidium. The Central Committee's also 'relieved' him of duties of the Presidium member on July 16, 1960. In October 1961, his political defeat was complete at the 22nd party congress when he was excluded from election to the Central Committee.
After the downfall of Khrushchev, Brezhnev returned Voroshilov to politics, in a figurehead role. He was reelected to the Central Committee (1966-1969) and was awarded a second medal of Hero of the Soviet Union (1968).
He died in 1969 in Moscow.