The ideological heirs of the Narodniks, the SRs won a mass following among the Russian peasantry by endorsing the overthrow of the Tsar and the redistribution of land to the peasants.

Meanwhile, Alexander Kerensky, one of the leaders of the February Revolution and the second and last head of the Provisional Government (July–November 1917) was a nominal member of the SR party but in practice acted independently of its decisions.

By November 1917, the Provisional Government had been widely discredited by its failure to withdraw from World War I, implement land reform or convene a Constituent Assembly to draft a Constitution, leaving the soviet councils in de facto control of the country.

The party's ideology was built upon the philosophical foundation of Russia's Narodnik–populist movement of the 1860s–1870s and its worldview developed primarily by Alexander Herzen and Pyotr Lavrov.

After a period of decline and marginalisation in the 1880s, the Narodnik–populist school of thought about social change in Russia was revived and substantially modified by a group of writers and activists known as neonarodniki (neo-populists), particularly Viktor Chernov.

In this way, with the economic spurt and industrialisation in Russia in the 1890s, they attempted to broaden their appeal in order to attract the rapidly growing urban workforce to their traditionally peasant-oriented programme.

Party leaders included Grigori Gershuni, Catherine Breshkovsky, Andrei Argunov, Nikolai Avksentiev, Mikhail Gots, Mark Natanson, Rakitnikov (Maksimov), Vadim Rudnev, Nikolay Rusanov, Ilya Rubanovich and Boris Savinkov.

These tactics were inherited from SRs' predecessor in the populist movement, Narodnaya Volya (“People's Will”), a conspiratorial organisation of the 1880s.

The SR Combat Organisation (SRCO), responsible for assassinating government officials, was initially led by Gershuni and operated separately from the party so as not to jeopardise its political actions.

SRCO agents assassinated two Ministers of the Interior, Dmitry Sipyagin and Vyacheslav von Plehve, Grand Duke Sergei Aleksandrovich, the Governor of Ufa N. M. Bogdanovich and many other high-ranking officials.

In 1903, Gershuni was betrayed by his deputy, Yevno Azef, an agent of the Okhrana secret police, arrested, convicted of terrorism and sentenced to life at hard labour, managing to escape, flee overseas and go into exile.

Other issues also divided the defectors from the PSR as Maximalists disagreed with the SRs' strategy of a two-stage revolution as advocated by Chernov, the first stage being popular-democratic and the second labour-socialist.

A smaller group, the internationalists, which included Chernov, favoured the pursuit of peace through cooperation with socialist parties in both military blocs.

Chernov also tried to play a larger role, particularly in foreign affairs, but he soon found himself marginalised and his proposals of far-reaching agrarian reform blocked by more conservative members of the government.

This weakening of the party's position intensified the growing divide within it between supporters of the pluralistic Constituent Assembly, and those inclined toward more resolute, unilateral action.

In August 1917, Maria Spiridonova advocated scuttling the Constituent Assembly and forming an SR-only government, but she was not supported by Chernov and his followers.

At the Second All-Russian Congress of Soviets on 25 October, when the Bolsheviks proclaimed the deposition of the Provisional government in Petrograd, the split within the SR party became final.

Dissatisfied with the large concessions granted to Imperial Germany by the Bolsheviks in the Treaty of Brest-Litovsk, two Chekists who were left SRs assassinated the German ambassador to Russia, Count Wilhelm Mirbach early in the afternoon on 6 July.

[13] Following the assassination, the left SRs attempted a "Third Russian Revolution" against the Bolsheviks on 6–7 July, but it failed and led to the arrest, imprisonment, exile and execution of party leaders and members.

Many SRs fought for the Whites or Greens in the Russian Civil War alongside some Mensheviks and other banned socialist elements.

Following Lenin's and Stalin's instructions, a trial of SRs was held in Moscow in 1922, which led to protests by Eugene V. Debs, Karl Kautsky, and Albert Einstein among others.