Mdivani joined the Bolshevik faction of the Russian Social Democratic Labour Party in 1903 and engaged in revolutionary activities in Tbilisi, Baku, Batumi, and other industrial centers of the Caucasus.
During the Russian Civil War, that followed the Russian Revolution of 1917, he was commissioned to the Caucasus Front where he worked for the Caucasian Bureau of the Central Committee of the Bolshevik Party and served as a member of the Revolutionary Military Council of the 11th Army.