Kun fought for Austria-Hungary in the First World War. He was captured as a prisoner of war and taken to Russia, where he became a Communist. Upon his release, he returned to Hungary, where the resources of a shattered government were further strained by refugees from lands lost under the Treaty of Trianon. Desiring to attempt a Communist revolution which lacking mass support could only be a coup, he communicated by telegraph with Russian Communist leader Vladimir Lenin.
On March 21, 1919, Kun and the small Communist Party made their move, establishing the second Communist government in Europe (after Russia itself). The government only lasted for 133 days. Rear Admiral Miklos Horthy, aided by anti-Communists from neighboring countries, crushed the Communists, and forced them to hand over power to a Social Democratic party.
Béla Kun then went into exile in Vienna, Austria, then also controlled by Social Democrats, and eventually made his way back to Russia. There he rejoined the Communist Party of the Soviet Union, and became a leading figure in the Communist International as an ally of Grigory Zinoviev. in this capacity he went to germany to advise the Communist Party there and sought to encourage that party to follow the theory of the offensive which he and Zinoviev supported.
He was killed in 1936, as part of Josef Stalin's purge of the Communist old guard.