In 2007, Onyshchenko was appointed as an assistant Minister for Emergencies and affairs in protection of population from the consequences of the Chernobyl Catastrophe (today State Emergency Service of Ukraine). He has served as a member of the Verkhovna Rada since 2012. In 2012 he was elected to parliament in electoral district 93 (located in Kyiv Oblast) for Party of Regions. In 2014 he was re-elected in the same district as an independent candidate. In parliament he became a member of the parliamentary faction People's Will. On 11 January 2021 Oleksandr Onyshchenko was put on US Sanctioned Persons list due to attempt to influence U.S. Presidential elections.