Mirkóczi was a member of the local representative body in Feldebrő from 2007 to 2010. Meanwhile, he joined Jobbik in 2008. He was elected vice-president then president of the party's Heves County branch. He also became president of the party's church affairs cabinet. He was elected a Member of Parliament via the Jobbik's national list in the 2010 Hungarian parliamentary election. He served as party spokesperson from June 2010. He ran for mayoral seat of Eger in the 2010 Hungarian local elections as a candidate of Jobbik, obtaining 12.39 percent of the vote. He was re-elected MP in 2014 and 2018, via the Jobbik's national list both times. He was again a mayoral candidate in his birthplace during the 2014 Hungarian local elections, obtaining 26 percent of the vote. He was a member of the parliament's National Security Committee from 2010 to 2019. He presided the aforementioned committee from 2018 to 2019. He was also a member of the Human Rights, Minority, Civil and Religious Affairs Committee for a brief time in 2010, and the National Defense and Law Enforcement Committee from 2012 to 2018.[2]
In 2012, Mirkóczki introduced a constitutional amendment to the Parliament seeking to ban "the promotion of sexual deviations". The amendment would punish the "promotion of homosexuality or other disorders of sexual behaviour" with up to eight years in prison. LMBT Federation, a Hungarian LGBT advocacy group, protested against the amendment and called on Parliament to reject it. The Democratic Coalition also voiced their opposition and called it "mean and shameful".[3] The amendment ultimately failed to pass.
Mirkóczki was elected mayor of Eger during the 2019 Hungarian local elections; he ran an independent under the banner United for the City Association (EVE) and his candidacy was supported by Jobbik, MSZP, DK, Momentum and LMP.[4] Mirkóczki defeated incumbent mayor and Fidesz candidate László Habis with 47.6 percent of the vote.[5] Mirkóczki left Jobbik in June 2020.[6] His mayoralty was marked by constant conflicts after he lost his majority in the assembly in October 2020. Those leaving blamed Mirkóczki's "authoritarian" leadership style.[7] The United for the City Association (EVE) excluded Mirkóczki from their faction in May 2021, and he was accused of starting to move closer to Fidesz during his mayoralty.[8] Mirkóczki, who ran as a candidate of the Civil Public Life Association (CKE), was defeated by Fidesz candidate Ákos Vágner in the 2024 Hungarian local elections.[9]