Bērzin returned to Russia after the February Revolution. At the 6th Congress of the Russian Social Democratic Labour Party (Bolsheviks), in August 1917, he was elected a full member of the Central Committee. He was one of the majority of the 21-member committee who backed Vladimir Lenin's line that the Bolsheviks should overthrow the Provisional Government and seize power. He was also a member of the Central Committee of the Social Democratic party of Latvia.