Liadov was first drawn to the populist Narodnik movement in Moscow in 1891. By 1893 he was involved in founding the Moscow Workers’ Union. Following his arrest in 1895 he was exiled to Verkhoiansk two years later. In 1902 he joined the Saratov Committee of the Russian Social Democratic Labour Party (RSDLP). However he emigrated in 1903, and attended the Second Congress of the RSDLP, joining the Iskra faction. The Central Committee of the party offered him a post following the Congress and in 1904 he attended the meeting of 22 Bolsheviks in Geneva where he was elected to the Bureau of the Committees of the Majority. He then attended the International Socialist Congress, Amsterdam 1904 as a Bolshevik delegate.
During the 1905 Revolution, Liadov fought at the barricades in Moscow and served as a member of the Moscow Committee of the RSDLP. He served as a delegate to the Third, Fourth, and Fifth Party Congresses. Between 1909 and 1911 he sided with the Otzovisty faction, and moved to Baku in 1911. In 1917 he was deputy chairman of the Baku Soviet and now sided with the Mensheviks. He took control of the newspaper Izvestiia Bakinskogo soveta. From 1918 to 1920 he was active in Georgia, only returning to Moscow in 1920. He was then readmitted into the Bolshevik Party and served on the Supreme Council of the National Economy.
From 1923 to 1929 Liadov was rector of the Sverdlov Communist University. Then he headed Glavnauka, but in 1930 he was appointed director of the Archive of the October Revolution and served as a member of the academic boards of the Lenin Institute and of Istpart. He attended the Twelfth through Sixteenth Party Congresses, becoming a member of the Central Auditing Commission at the Fifteenth Party Congress. Liadov was also a candidate member of the All-Russian Central Executive Committee and the Central Executive Committee of the USSR. His history of the party, first published in 1906-07, was reissued in 1923-26. Liadov retired with a special pension in 1932.