On 10 April 1918, Manner was appointed commander-in-chief of the Red Guards as well as head of state of its short-lived government, The People's Deputation.

[7] After the civil war, Manner fled to Soviet Russia where he became the second chairman of the Finnish Communist Party (SKP) after Yrjö Sirola.

Manner and his wife Hanna Malm's fall from grace began in 1929 when they lost a briefcase containing secret documents while in Stockholm.

While many communists believed it provided an opportunity to recruit more workers to their cause and incite them to revolution, Manner remained passive.

Comintern reprimanded the party for inaction, and while Manner personally survived with minor criticism, Hanna Malm was excluded from the central committee.

The theory they came up with pointed the finger at Manner himself and other leaders of the Finnish Social Democratic Party (SDP), who had reacted to the revolutionary moment too slowly, as well as at the Bolsheviks.

Manner retracted his opinion quickly, but Malm directly named Comintern Executive Committee member Otto Wille Kuusinen as one of the former SDP leaders in question.

[10] In 1935, Manner and Malm were arrested after a raid in their apartment found weapons and books by renounced Bolsheviks Nikolai Bukharin, Leon Trotsky and Grigory Zinoviev.

According to professor of history Alexander Popov, the real cause of death could be attributed to radiation sickness, which Manner could have received, since he worked with water containing radium.