During his studies he joined the Russian Social Democratic Labour Party and organized an underground network for importing and distributing political literature.

Uritsky played a leading role in the Bolsheviks' armed take-over in October and was later made head of the Petrograd Cheka secret police.

In this position Uritsky coordinated the pursuit and prosecution of members of the nobility, military officers, rival socialists, ranking Russian Orthodox Church clerics, and anyone who opposed the Bolsheviks.

On March 4, 1918, the Petrograd committee published the first number of the journal Kommunist, the public organ of the "left communist" opposition, as directed by Radek and Uritsky.

On May 25, 1918, with the Revolt of the Czechoslovak Legion, the Russian Civil War began and Uritsky resumed his position on the Central Committee.

[3][4] Following this event, along with the assassination attempt on Lenin by Socialist Revolutionary Fanny Kaplan on August 30, the Bolsheviks began a wave of persecution known as the Red Terror.