He was a member of the National Assembly of Serbia from 2004 to 2008, served three terms as mayor of the Belgrade municipality of Grocka, and was the chair of Serbian Railways from 2012 to 2014.
[5] The Radicals won eighty-two out of 250 seats in the 2003 election, emerging as the largest single party in the national assembly but falling well short of a majority; they ultimately served in opposition in the parliament that followed.
Serbia's election system was reformed in 2011, such that parliamentary mandates were awarded in numerical order to candidates on successful lists.
Simonović became mayor of the municipality for the first time on 23 June 2005 when a new local coalition government was formed, although he left the position on 4 November of the same year after further political re-alignment.
Simonović led the Progressive list to a plurality victory with eleven out of thirty-five seats in Grocka in the 2012 local elections.
[32] Shortly after his appointment, he said that Serbian trains and lines would be modernized in the next five years thanks to a planned Russian loan of $800 million dollars.
[33] In early 2014, he announced the launch of electric train service from Kraljevo to the northern part of Kosovska Mitrovica, in the disputed territory of Kosovo.
In late 2013, the Union of Railways Workers of Serbia called for his removal, citing poor labour-management relations and a series of problems affecting the company.
[35] In February 2014, workers from the union reiterated their demands in a protest outside the administrative building of Serbian Railways, citing what they described as significant company losses due to corruption.
[37] On 12 December 2018, the house of Grocka journalist Milan Jovanović was set on fire after a Molotov cocktail was thrown through a window in his garage.
The verdict issued by Judge Slavko Žugić found that Simonović had encouraged police officer Vladimir Mihailović to send a warning to Jovanović by burning the latter's car; Mihailović, in turn, incited Igor Novaković to commit the crime, and Novaković hired Aleksandar Marinković to actually carry out the arson attack.