After the October coup in Petrograd, the SDP declared a general strike under the slogan “We demand”, but did not attempt to seize power in Finland despite the calls of Vladimir Lenin. After the Seim approved the laws on an 8-hour working day and the democratization of the municipal election system, the strike was stopped. On November 14 (27), the Seim declared itself independent from the Russian authorities and appointed a new government headed by Pehr Evind Svinhufvud. On November 23 (December 6), the Finnish Parliament adopted the Declaration of Independence. December 18 (31), the Council of People’s Commissars of Soviet Russia led by Vladimir Lenin recognized the independence of Finland (Finnish Social Democrats participated in the development of the draft declaration). On December 22 (January 4), the decree on independence was approved by the All-Russian Central Executive Committee (VTSIK).
In the late 1917 – early 1918, political confrontation in Finland was growing. Radical members of the SDP began preparing for the revolution. Workers’ (Red) guards were formed and actively operated in the country. In January 1918, at a meeting of the SDP Council, the Executive Committee of Finnish Workers was formed, which prepared a plan for seizing power. On the night of January 15 (28), 1918, a red banner was raised over the Seim. The SDP Council declared the Svinhufvud government deposed and formed a Finnish People's Delegation headed by Kullervo Manner. Oskari Tokoi headed the Department of Food, Otto Kuusinen headed Education, and Yrjö Sirola headed Foreign Affairs. The southern part of the country was under the control of the Reds. Soviet Russia immediately tried to build interstate relations with the Finnish Socialist Workers’ Republic.
The Svinhufvud government fled to the north of the country to Vaasa, concluded a treaty with Germany, and called for German troops to Finland. With their help, the opponents of the Reds led by Carl Gustaf Mannerheim won the civil war in Finland, which lasted until May 1918. The Red Government fled to Petrograd.
After the defeat of the revolution, the SDP collapsed. In August 1918, representatives of the left-wing (Otto Kuusinen, Yrjö Sirola) formed the Communist Party of Finland in Moscow. In 1919, the SDP was reorganized under the guidance of the right-wing leader Väinö Tanner (in January 1918, he condemned the coup, held a neutral position during the civil war) and won 80 seats in the newly elected Parliament. Further on, the SDP became one of the key political parties in Finland.