Under the leadership of Lenin, the Bolshevik Party seized power in the Russian Republic with the Communist coup d'état known as the October Revolution. Overthrowing the Russian Provisional Government, the Bolsheviks established a new government, the first Council of People's Commissars, with Lenin as chairman. Ruling by decree, Lenin’s Sovnarkom introduced widespread reforms, such as confiscating land for redistribution among the peasantry, permitting non-Russian nations to declare themselves independent, improving labour rights, and increasing access to education.

The Lenin party continued with the previously scheduled November 1917 election, but when it produced a Constituent Assembly dominated by the rival Socialist Revolutionary Party the Bolsheviks lambasted it as counter-revolutionary and shut it down. The Bolshevik government banned a number of centrist and right-wing parties, and restricted the activities of rival socialist groups, but entered into a governmental coalition with the Left Socialist Revolutionary Party. Lenin had inherited a country in the midst of the First World War, with war-weary Russian troops battling the Central Powers of Germany and Austria-Hungary on the Eastern Front. Deeming the ongoing conflict a threat to his own government, Lenin sought to withdraw Russia from the war, using his Decree on Peace to establish an armistice, after which negotiations took place resulting in the Treaty of Brest-Litovsk. This punitive treaty – highly unpopular within Russia – established a cessation of hostilities but granted considerable territorial concessions to Germany, who took control of large areas of the former Empire.

Consolidating power: 1917–1918

Constitutional and governmental organization

The previous Provisional Government had agreed for a Constituent Assembly to be elected in November 1917; after taking power, Lenin – aware that the Bolsheviks were unlikely to attain a majority – wanted to postpone this election, but other Bolsheviks disagreed, and thus the election took place as scheduled. In the election for the Constituent Assembly, the Socialist Revolutionaries were elected as the largest party, with the Bolsheviks coming second with approximately a quarter of the vote. According to Lenin biographer David Shub, this had been "the freest election in [Russia's] history" up till that time. During the vote, the Bolsheviks had achieved their best result in the cities, industrial areas, and military garrisons in the centre of Russia, while their anti-war message had proved particularly popular with soldiers and sailors. Lenin and other supporters felt that the vote had not been a fair reflection of the Russian people's democratic will, believing that the population had not had the time to acquaint themselves with the Bolsheviks' political program and noting that the candidacy lists had been drawn up before the Left Socialist-Revolutionaries had split from the Socialist-Revolutionaries.

The newly elected Russian Constituent Assembly convened in Petrograd in January 1918. However, the Bolsheviks publicly argued that the Constituent Assembly was counter-revolutionary because it sought to remove power from the soviets, an idea that the Mensheviks and Socialist-Revolutionaries argued against. When campaigners marched in support of the Constituent Assembly in Petrograd they were fired upon by soldiers, resulting in several deaths. Intent on discrediting the Assembly, the Bolsheviks presented it with a motion that would have stripped the Assembly of much of its legal powers; the Assembly members rejected this. The Bolshevik government claimed this as evidence that the Assembly was counter-revolutionary and disbanded it by force.

There were repeated calls for the Bolsheviks to welcome socialists from other parties to join Sovnarkom, however Lenin resolutely opposed this idea; in November 1917 a number of members from the Bolshevik Central Committee resigned in protest. Moreover, Russia's largest trade union, the Union of Railroad Employees, threatened to go on strike unless a pan-socialist coalition government was formed. However, the Bolsheviks did court the support of the Left Socialist-Revolutionaries, a group who had splintered from the main Socialist-Revolutionary Party and who were more sympathetic to the Bolshevik administration; on 9 December 1917 the Left Socialist-Revolutionaries became junior partners in a coalition with the Bolsheviks, being given five posts in the Sovnarkon cabinet. This resulted in what Lenin biographer Dmitri Volkogonov termed "a rare moment of socialist pluralism" in Soviet history.

In November 1917 Lenin and his wife took a two-room flat within the Smolny Institute, with Trotsky and his family living in the flat opposite; being based here allowed Lenin to devote himself to the revolutionary government. The stress of this position exacerbated Lenin's health problems, in particular his headaches and insomnia. In December, he and Nadezdha left Petrograd for a holiday at the tuberculosis sanatorium at Halila in Finland – now officially an independent nation-state – although returned to the city after a few days. In January 1918 he survived an assassination attempt made on him in the city; Fritz Platten, who was with Lenin at the time, shielded him but was injured by a bullet. Sources differ regarding who was to blame, with some identifying the culprits as disaffected Social-Revolutionaries, and others as monarchists.

In the spring of 1918, Sovnarkom officially divided Russia into six oblasti, or territorial entities – Moscow, the Urals, North, Northwest, West Siberia, and Central Siberia – each with their own quasi-sovereign status. These oblasti were governed by socialist intelligentsia, and held their own Congresses of Soviets. In part this division served to facilitate the central control of the various regional soviets, many of which had taken over de facto control of their own areas. The oblasti in turn were divided into smaller provinces, the gubernii, a number of which proclaimed themselves to be "republics", and some of the non-Russian peoples living within Russian territory, such as the Bashkirs and Volga Tatars, formed their own "national republics".

At the 7th Congress of the Bolsheviks in March 1918, the group renounced their official name, the "Russian Social Democratic Labor Party", with Lenin believing that the term "Social Democratic" was too closely associated with the Social Democratic Party of Germany, who had endorsed Germany’s entrance into the war. Instead they renamed themselves the Russian Communist Party, emphasizing their ultimate goal: the establishment of a future communist society. Although ultimate power officially wrested with the country's government in the form of Sovnarkom and the Executive Committee elected by the All-Russian Congress of Soviets, the Communist Party was the de facto controlling power in Russia, something which was acknowledged by its members at the time. Within the party was established a Political Bureau ("Politburo") and Organisation Bureau ("Orgburo") to accompany the preexisting Central Committee. The decisions made by these three party bodies were considered mandatory for the state apparatus of the Sovnarkom and Council of Labor and Defense to adopt.

Lenin was the most significant figure in this governance structure; as well as being the Chairman of Sovnarkom and sitting on the Council of Labor and Defense, he was on the Central Committee and Politburo of the Communist Party. The only individual to have anywhere near this influence was Lenin's right-hand man, Yakov Sverdlov, although the latter died in March 1919 during a flu pandemic. However, in the Russian public imagination it would be Leon Trotsky who was usually seen as the second-in-command; although Lenin and Trotsky had had differences in the past, after 1918 Lenin came to admire Trotsky's skills as an organizer and his ruthlessness in dealing with the Bolsheviks' enemies. Within this Bolshevik inner circle, it was Zinoviev and Kamenev who were personally closest to Lenin.

During this period, the party itself had witnessed massive growth; while it had 23,600 members in February 1917, this had grown to 250,000 by 1919, and it would again rise to 730,000 in March 1921. Lenin recognised that many of these new members were careerists seeking to advance their own positions rather than those who shared the Bolsheviks' ideological vision; in June 1921 he ordered a re-registration process of members in order to weed out perceived unreliable elements. In July 1918, at the Fifth All-Russian Congress of the Soviets, a constitution was approved that reformed the Russian Republic into the Russian Soviet Federative Socialist Republic.

Social and economic reform

Lenin's new regime issued a series of decrees, the first of which was a Decree on Land; drawing heavily upon the Socialist-Revolutionary Party's platform, it declared that the landed estates owned by the aristocracy and the Russian Orthodox Church should be confiscated, taken into national ownership, and then redistributed among the peasants by the local government. This was accompanied by the Decree on Peace, in which the Bolsheviks called for an end to the First World War. These two decrees exacerbated the problem of desertion from the Russian Army, as increasing numbers of soldiers left the Eastern Front and returned to their homes, where they intended to claim land. In November the Bolshevik government issued the Decree on the Press which closed down many opposition media outlets which were deemed counter-revolutionary; the decree was widely criticised, including by many Bolsheviks themselves, for compromising freedom of the press, although Sovnarkom claimed that it would only be a temporary measure. On 1 December, Sovnarkom outlawed the Constitutional Democratic Party.

On 29 October, Lenin released a Decree restricting the work day to eight hours. That same day he proclaimed the Decree on Popular Education which stipulated that the Bolshevik government would guarantee free, secular, universal education for all children in Russia. On 2 November, Lenin issued the Declaration of the Rights of the Peoples of Russia, which stated that non-Russian ethnic groups living inside the Empire had the right to cede from Russian authority and establish their own independent nation-states. Many nations declared independence as a result of this: Finland and Lithuania in December 1917, Latvia and Ukraine in January 1918, Estonia in February 1918, Transcaucasia in April 1918, and Poland in November 1918. Independent communist parties were established in each of these countries with the support of Sovnarkom, which held a Conference of Communist Organisations of the Occupied Territories in Moscow 1918. The government officially converted Russia from the Julian calendar to the Gregorian calendar used in Europe. Over the coming years, laws were introduced that helped to emancipate women, by giving them economic autonomy of husbands and removing restrictions on divorce.

On 30 November they issued an order requisitioning the country's gold, and nationalised the banks, an act which Lenin saw as a major step toward establishing socialism. That same month witnessed a major overhaul of the Russian armed forces, as Sovnarkom implemented egalitarian measures by abolishing all previous ranks, titles, and medals; to reorganise the system, soldiers were called upon to establish their own committees through which they could elect their own commanders. On 14 November, Lenin issued the Decree on Workers' Control, which called on the workers of a particular enterprise to establish an elected committee who would monitor that enterprise's management.