He joined the CPSU in 1939, he was the head of department, secretary of the Soviet District Committee of the All-Union Communist Party of Bolsheviks of Moscow.

In 1950, he was Deputy head of the department of Propaganda and Agitation of the Moscow City Committee of the All-Union Communist Party of Bolsheviks.

In 1965, he replaced Leonid Ilyichev as Secretary of the CPSU Central Committee, in charge of issues of ideology, history and culture.

According to Vasily Ogryzko, Demichev “was considered a member of Alexander Shelepin’s team ,” while “in his heart he supported the Russian party in literature and art and terribly disliked liberals”.

Sharing some of the views of the “ soil people ” he patronized Ilya Glazunov and Vladimir Soloukhin.