Frinovsky was actively involved in the Great Purge and personally led the mass arrests and executions of security and military officials across the Soviet Union from 1937 to 1938.

[2] He subsequently joined an anarchist group and began working as an accountant at a military hospital..[2] In March 1917, during the February Revolution, Frinovsky took part in the assassination of Major-General Mikhail Antonovich Bem, a distinguished army officer who was suppressing anti-war protests in Penza.

A month later, when the October Revolution occurred, the Red Guard unit under his command participated in storming of the Kremlin during the Moscow Bolshevik Uprising.

Frinovsky was made a commissar of a combat unit and also head of the Special Section (the political supervisor and representative of the Cheka, the Bolshevik secret police) of the 1st Cavalry Army.

In this capacity, he participated in many operations most vital for survival of the Bolshevik regime, including actions against anarchists and rebel militias in Ukraine.

On 17 February 1938, he supervised the murder of the head of the NKVD Foreign Department, Abram Slutsky, who was chloroformed and injected with lethal poison in Frinovsky's office.

This purge resulted in execution of 16 senior NKVD officials, who were shot, and Marshal of the Soviet Union Vasily Blyukher, the commander of the Far Eastern Army.

[7] While Frinovsky was in the Far East, Stalin proposed that he be appointed People's Commissar for the Navy, an apparent promotion, which was actually part of a manoeuvre to remove Yezhov.

On 25 August, Frinovsky arrived back in Moscow and effectively ran the NKVD for a few days, while Beria was in Georgia arranging who would take over from him there and Yezhov was in a state of drunken depression.

He seized the opportunity to execute a group of former NKVD officers, including Leonid Zakovsky and Sergei Naumovich Mironov, to prevent them giving evidence against him to Beria.

[8] On 8 September 1938, Frinovsky was named People's Commissar for the Navy, and was sufficiently in favour to be among the guests at a lunch in the Kremlin on the 21st anniversary of the Bolshevik revolution, at which Stalin and Beria were present, but Yezhov was excluded.

It was standard procedure that the condemned were photographed prior to execution: the last pictures of Frinovsky's wife and son are in David King's book,Ordinary Citizens.