Mitrović received the 119th position on the Radical Party's electoral list in the 2003 Serbian parliamentary election. The party won eight-two seats, becoming the largest single party in the assembly but falling well short of a majority and ultimately serving in opposition. Mitrović was not initially included in the party's assembly delegation but received a mandate on February 17, 2004, as the replacement for a party colleague who had been appointed to the Assembly of Serbia and Montenegro. He served in parliament for the next three years. He was again included on the Radical Party's list for the 2007 parliamentary election but was not included in its assembly delegation in the parliament that followed.
The RadicalParty experienced a serious split in 2008, with several members joining the breakaway Serbian Progressive Party under the leadership of Tomislav Nikolić and Aleksandar Vučić. Mitrović sided with the Progressives. Serbia's electoral system was reformed in 2011, such that parliamentarymandates were awarded in numerical order to candidates on successful lists. Mitrović received the 148th position on the Progressive Party's Aleksandar Vučić — Future We Believe In coalition electoral list in the 2014 Serbian parliamentary election and was elected when the list won a majority with 158 out of 250 mandates. He was promoted to the 133rd position on the successor Aleksandar Vučić – Serbia Is Winning list in the 2016 election. He narrowly missed direct re-election when the list won a second consecutive majority with 131 seats, but was able to take his seat in the assembly on August 10, 2016, as a replacement for the author Ljiljana Habjanović Đurović, who had been elected on the Progressive list but declined her mandate. Mitrović currently serves as a deputy member of the assembly's defense and security committee, the committee on the diaspora and Serbs in the region, and the committee on Kosovo-Metohija. He is a member of the parliamentary friendship groups with Belarus and Kazakhstan. He is the president of the Progressive Party's local organization in Bujanovac and is a member of the municipal assembly.
