Following the Russian Civil War, he enrolled at the school of the Moscow Art Theatre, where his classmates included Mikhail Kedrov and Boris Livanov.

Yanshin's first notable roles at the Art Theatre were as Dobchinsky in Gogol's The Government Inspector and as the footman Petrushka in Griboyedov's Woe from Wit.

He came to greater attention in the role of Lariosik in Bulgakov's Days of the Turbins, and thereafter began to receive work in other theaters.

In 1963 Yanshin was criticized by the Soviet ministry of culture, which disapproved of his staging contemporary, non-traditional plays; he resigned and returned to the Moscow Art Theatre, where he was instrumental in the hiring of the director Oleg Yefremov.

They divorced in 1934, and that same year Yanshin married Nadezhda Kiselyova (stage name Lyalya Chyornaya), a dancer at the Rumen Theatre.