After Joseph Stalin’s death in March 1953 and the execution of the powerful state security chief, Lavrenty Beria—which Khrushchev engineered—Nikita Khrushchev engaged in a power struggle with Georgy Malenkov, who was Stalin’s heir apparent.

Khrushchev soon gained the decisive margin by his control of the Soviet Communist party machinery. In September 1953 he replaced Malenkov as first secretary.

Main source: Britannica