During the Russian Civil War, he was chief political commissar and member of the Revolutionary Military Council of the 7th Army of the Western Front.
According to Victor Serge, who was in Petrograd while it was in 'mortal peril' from the White Army of General Yudenich: The city was saved mainly through Grigori Yevdokimov, an old seafarer, vigorous and grey-haired, with a mujik's roughness.
During the power struggle that followed the death of Vladimir Lenin in 1924, Yevdokimov backed Grigory Zinoviev against Leon Trotsky, and then against Joseph Stalin.
In January 1925, he backed a resolution proposed by another Zinoviev supporter, Pyotr Zalutsky to expel Trotsky from the communist party, and when this was blocked by Stalin and others, he complained that they were "too soft".
Yevdokimov submitted a long, written complaint about what he called "the massacre of the Leningrad organisation" conducted after the congress, in which he alleged that more than 200 party members had been exiled from the city to remote parts of Northwestern Russia, and more than 1,500 others – including Zinoviev – had been sacked from their posts.
[4] After the unification of the supporters of Leon Trotsky and Grigory Zinoviev, which took place in the spring of 1926, Yevdokimov became an active participant in the "United Opposition."
He was readmitted to the party and a minor post managing the dairy industry Police raided Yevdokimov's apartment on 8 December 1934, eight days after the assassination of Sergei Kirov, and found numerous documents and leaflets dating from his time as an active oppositionist.