From late 1921 until the end of his life in 1935, Mickevičius lived in Moscow. He was a delegate to the Second through Sixth Congresses of the Comintern. Working on the Executive Committee of the Comintern from 1923 to 1935, he became a candidate member of the Executive Committee of the Comintern in 1924 and a member in 1928. Kapsukas was a delegate to the Eleventh, Twelfth, and Fourteenth through Seventeenth RCP(b) Congresses. He was elected a candidate member of the Central Committee of the RCP(b) at the Eighth Congress (1919).