Grigory Zinoviev was born in Kherson governorate into the family of a dairy farm owner. His real name was Ovsey-Gersh Radomyslsky. He was home-educated. In the 1890s, Zinoviev led workers’ circles, took part in the preparation of workers’ strikes in the south of Russia. He had to repeatedly stay overseas hiding from police harassment, and briefly studied at the University of Bern. Since 1901, Zinoviev was a member of the Russian Social Democratic Labour Party (RSDLP), since 1903, a Bolshevik. One of his Party pseudonyms was Zinoviev. During the revolution of 1905–1907, he returned to Russia and was elected a member of the St. Petersburg Committee of the RSDLP. The 5th Congress of the RSDLP in London (1907), elected him to the Central Committee of the Party. In October 1908, he joined the editorial team of the Bolshevik newspaper Proletary [Proletarian] in Geneva, Switzerland, together with Vladimir Lenin and Leon Kamenev. He was an organizer of the Prague Conference of the RSDLP (1912) and was elected a member of the Central Committee. Together with Lenin, Zinoviev represented the Bolsheviks at the International Socialist Conferences in Zimmerwald (1915) and Kienthal (1916).

After the February Revolution of 1917, he returned to Petrograd along with Lenin and a group of Bolsheviks. He entered the editorial team of Pravda [Truth] newspaper. He was one of the best Bolshevik propagandists, who gave speeches and delivered lectures. After the July political crisis of 1917, together with Lenin Zinoviev was hiding to avoid arrest in Razliv near Petrograd (July–August 1917). On October 10, 1917, at a closed meeting of the Bolshevik Central Committee, together with Leon Kamenev he objected to the resolution on an armed uprising. After the October coup of 1917, he supported the idea of a unified socialist government with the Mensheviks and Socialist-Revolutionaries. Zinoviev announced his withdrawal from the Central Committee in November 1917 due to disagreement with Lenin’s policy. Later he assumed, it had been a mistake.

From December 1917 to March 1918, he held the post of Chairman of Petrograd Soviet of Workers’ and Soldiers’ Deputies. In January 1918, he headed the Committee for Revolutionary Defense of Petrograd. After the Government moved to Moscow in March 1918, Zinoviev headed the Council of Commissars of the Petrograd Labour Commune, from May 1918 to February 1919, he headed the Council of Commissars of the Union of Communes of the Northern Region. He participated in the organization of the Red Terror in Petrograd. Since January 1919, Chairman of the Workers’ Defense Committee of the Northern Region, since May 1919, Chairman of the Committee for the Defense of Petrograd and Petrograd governorate. A member of the Revolutionary Military Council of the 7th Army. He supervised the defense of Petrograd against the troops of Nikolay Yudenich.

In 1919–1926, Zinoviev was Chairman of the Petrograd (since 1924, Leningrad) Soviet, Chairman of the Executive Committee of the Communist International. In 1921–1926, he was a member of the Politburo of the Central Committee of the Communist Party of the Bolsheviks. After the death of Vladimir Lenin, he was among the main contenders for power in the party and country, an active participant in the internal party struggle of the 1920s.

In 1934, he was arrested and sentenced to ten years of imprisonment over the case of Moscow Center. On August 24, 1936, Zinoviev was sentenced to death over the case of the Anti-Soviet United Trotsky-Zinoviev Center. He was shot on August 26. In 1988, Zinoviev was rehabilitated.