In May 2017, he was appointed Minister without Portfolio in the Third Orbán Government, responsible for the planning, construction and commissioning of the two new blocks at Paks Nuclear Power Plant.
Süli was appointed chief executive officer (CEO) of the Paks Nuclear Power Plant on 24 March 2009, replacing József Kovács, who held the position since 12 January 2005.
After the 2010 parliamentary election, he was dismissed and was demoted to the office of Deputy CEO, working in this capacity until 2011, when he left the state-owned company after thirty years.
[4] Despite his replacement as CEO of the Paks Nuclear Power Plant in September 2010, Süli is considered as a right-wing, conservative-minded provincialist, who had extensive ties with the local branch of the Fidesz.
However the national leadership of the governing party announced in the next month that they chose György Kozmann, a former Olympic sprint canoeist as their candidate.
[11] János Süli was appointed as individual MP candidate of the governing coalition Fidesz–KDNP for Tolna County Constituency III (Paks) during the 2018 parliamentary election, replacing incumbent Fidesz parliamentarian Ferenc Hirt.
His portfolio for the construction of the Paks Nuclear Power Plant was subordinated to the Ministry of Foreign Affairs and Trade in the Fifth Orbán Government.
[15] Süli resigned from his position on 5 September 2022, after Szijjártó criticized the slow progress of the expansion investment of the Paks nuclear power plant.