When the war ended he became Finland's leading Social Democratic Party (SDP) politician, and a strong proponent of the parliamentary system.

[5] Väinö Tanner's legacy is in his directing the Finnish working class from their extremist ideology towards pragmatic progress through the democratic process.

Under his leadership the Social Democrats were trusted to form a minority government already less than 10 years after the bloody civil war.

Tanner's minority socialist government passed a series of important social reforms during its time in office, which included a liberal amnesty law, reduced duties on imported foods, and pension and health insurance laws.

Väinö Tanner's leadership was very important in forming the grounds and creating the Spirit of the Winter War which united the nation.

[8] After the Continuation War, and while still in prison, Tanner became the virtual leader of a faction of the SDP which had strong support from the US.

Only with the blessing of a long-serving parliamentarian was the presidency allowed to be represented by an aide-de-camp and wreath at Tanner's funeral.

Tanner met his future wife Linda (née Anttila; 1882–1978) in 1907 at a meeting of the Social Democratic Association of Students.