Member of the Verkhovna Rada of Ukraine of the IV-VII convocations, member of the Party of Regions faction (since December 2012), member of the Committee on Agrarian Policy and Land Relations (since December 2012); member of the political council of the Party of Regions. Candidate for the post of President of Ukraine at the early elections on 25 May 2014 (withdrew his candidacy). He has been repeatedly criticised for Ukrainophobia and separatism, and is on the national criminal wanted list.

On 3 June 2014, the Verkhovna Rada approved the prosecution, detention and arrest of Tsarev and his detention. However, he was later released.

On 26 June 2014, he was elected "speaker of the parliament" of the so-called Novorossiya, a union of the Russian-controlled DPR and LPR groups, which the Prosecutor General's Office of Ukraine classifies as terrorist. It is related to the "Committee for the Salvation of Ukraine", established in Moscow on 3 August 2015 by former high-ranking Ukrainian officials during the Yanukovych presidency.

After the full-scale Russian offensive against Ukraine, since March 2022, he has been suspected of collaborating with Russia and the Russian occupiers.

He actively participated in Russian propaganda video filming in the occupied territories of Kyiv region.

In March 2022, he offered the head of the military administration of Kryvyi Rih, Oleksandr Vilkul, to surrender the city to the Russian occupiers, but was refused. 

On 27 October 2023, the media reported that Oleg Tsarev was assassinated while he was staying at the Kirov Sanatorium in Yalta. According to media reports, Tsarev was hit with two shots and his condition was "very serious". The SBU took responsibility for eliminating the collaborator.