Rykov joined the Russian Social Democratic Labour Party (RSDLP) in 1898 and supported its Bolshevik faction when the party split into Bolsheviks and Mensheviks at its Second Congress in 1903. He worked as a Bolshevik agent in Moscow and Saint Petersburg and played an active role in the Russian Revolution of 1905. He was elected a member of the Party's Central Committee at its 3rd Congress (boycotted by the Mensheviks) in London in 1905 and its 4th Congress in Stockholm in 1906. He was elected candidate (non-voting) member of the Central Committee at the 5th Congress in London.