After his release from prison in 1905, Paul Milyukov, the famous Russian historian, founded the Constitutional Democratic Party (Cadets). Most of the early members were liberals from the propertied classes who favoured political reform. Initially critical of the Duma, Milyukov and other members of the party, eventually agreed to stand for election.

The Cadets were strong supporter of Russia's involvement in the First World War. In 1915 they began criticizing the war effort and questioned the competence of Nicholas II as the country's commander-in-chief. In one speech in the Duma, Paul Milyukov listed the failings of the government and asked if the explanation was stupidity or treason.

There were five Cadet cabinet ministers in the first Provisional Government. The party strongly opposed the Bolsheviks during the October Revolution. The Cadets, like other anti-Bolshevik parties, were banned by the Soviet government in 1918.