Tsarist police arrested him and he spent over seven years at hard labor in Siberia. In 1917, Myasnikov was active in factory committees, the soviet, and the Bolshevik party in his hometown of Motovilikha and in Perm. Gabriel Myasnikov is known as the execution initiator and killer of the Grand Duke Michael Alexandrovich of Russia (1918).
Myasnikov was a Left Communist in 1918, opposed to the Treaty of Brest-Litovsk. He was dissatisfied with elements of Party policy toward workers, but he did not support the Workers Opposition in 1920-21. Myasnikov disagreed with the Workers' Opposition's call for unions to manage the economy.
Instead, in a 1921 manifesto, Myasnikov called for “producers’ soviets” to administer industry and for freedom of the press for all workers. Leaders of the Workers Opposition Alexander Shlyapnikov and Sergei Medvedev feared that Myasnikov's proposals would give too much power to peasants. Despite their disagreements, however, they supported Myasnikov's right to voice criticisms of Party policy.
In February 1922, Myasnikov was expelled from the Russian Communist Party. In 1923, he formed an opposition faction called “Workers Group of the Russian Communist Party” that opposed the New Economic Policy. Party leaders arrested Myasnikov in May 1923, but then released him and attempted to isolate him from his support base by assigning him to a trade mission in Germany in 1923.
There Myasnikov formed ties to the Communist Workers' Party of Germany, a group at odds with the Russian Communist Party. These groups helped him publish the Manifesto of the Workers Group, without permission from the Russian Communist Party. Workers' Group was suppressed and later in 1923 Myasnikov was persuaded to return to Russia, where he was arrested and imprisoned.
In 1927, his sentence was changed to internal exile in Yerevan, Armenia. In 1928, he fled the USSR for Iran. He was arrested in Iran and then deported to Turkey.
In 1930, he immigrated to France, where he worked in factories until 1945. In 1945, the Soviet secret police returned Myasnikov to the USSR, where he was executed.