After Russia's large-scale invasion of Ukraine, Stremousov took a pro-Russian stance. On 16 March 2022, in the building of the Kherson Regional Council, he led an illegal meeting of a pseudo body of the Russian occupation administration together with local collaborators of the "Committee of Salvation for Peace and Order". The committee aimed to convince the residents of the region that the Ukrainian state had lost its ability to govern the region and called for support for the Russian occupation.

On 17 March 2022, the Kherson Regional Prosecutor's Office opened procedural management against Stremousov in criminal proceedings initiated on the fact of providing assistance to a foreign state in conducting subversive activities against Ukraine, committed under martial law (part 2 of article 28, part 2 of article 111 of the Criminal Code of Ukraine).

In particular, Kirill Stremousov threatened "dissidents" in occupied Kherson with Russian imprisonment. Also in his video message, Stremousov promised a "census" and punishment for "those who lived on grants".

Stremousov also promised to introduce the Russian ruble into monetary circulation in the occupied territory from 1 May 2022, however, despite his loud statements, the Ukrainian hryvnia remained in circulation[38].

On 11 May 2022, Stremousov stated that the occupation administration would request the incorporation of Kherson Oblast into the Russian Federation without a referendum as a full-fledged region. Subsequently, leaflets appeared en masse in Kherson announcing a reward of half a million hryvnias for Stremousov's head. After that, Stremousov fled from Kherson to temporarily occupied Donetsk.

On 9 November 2022, Russian media, citing Stremousov's driver and sources in law enforcement agencies, reported Stremousov's death in a traffic accident near Genichesk. At 7pm, the same day, confirmation of Kirill Stremousov's death was received from the so-called "Ministry of Health of the Kherson region". Stremousov's death occurred two days before the liberation of Kherson.