On 11 March 2007, Marchenko was elected deputy of the Legislative Assembly of Saint Petersburg of the 4th convocation.

On 24 May 2013 he again received a mandate for the Legislative Assembly of Saint Petersburg where he suggested initiatives to ban nightclubs, cancel mass events to celebrate the New Year due to the threat of terrorist attacks, to increase criminal liability for crimes committed by foreigners, to ban the sale of alcohol at night in public places.

[2][3] In 2015, Marchenko defended his MA dissertation at the History department of the Saint Petersburg State University.

A year later, journalists of the Novaya Gazeta found out that the originality level of the work is only 28%.

According to the party representatives, Marchenko thus violated the norms of the charter and the provision on the faction.