In 1907 Krylenko was arrested and exiled to Lubin in Russian Poland. He returned to St. Petersburg and in 1911 began contributing to pro-Bolshevik newspaper, Zvezda. Later he joined the editorial board of Pravda.
Krylenko travelled to Berne, Switzerland, in March, 1914, to participate in a conference held by the Social Democratic Labour Party. On his return he was arrested and drafted into the Russian Army. He served on the South-Sestern Front where he persuaded a large number of soldiers to join the Bolsheviks.
After the abdication of Nicholas II he returned to the capital where he joined the executive committee of the Petrograd Soviet and the Party Central Committee. Vladimir Lenin appointed him military commissar and he played the leading role in capturing Stavka, the command headquarters of the Russian Army.
As president of the supreme tribunal he prosecuted all the major political trials of the 1920s. In 1931 Joseph Stalin appointed Krylenko as Commissar for Justice and was involved in the conviction of a large number of members of the Communist Party during the Great Purges. Nikolai Krylenko was himself arrested and executed for treason in 1938.