At the age of seventeen, Kiss joined the Hungarian Socialist Party (MSZP) in 1996. Since 2008, he is the executive vice-president of the party's local branch in Óbuda, he was a member of the party's presidium in Budapest between 2010 and 2018. He was elected chairman of the National Ethics and Coordination Committee of the Socialist Party in 2018. Kiss was a member of the municipal assembly of Óbuda-Békásmegyer from 2006 to 2014.
Kiss was elected a Member of Parliament for Óbuda-Békásmegyer in the 2014 parliamentary election, defeating incumbent MP Erzsébet Menczer, the candidate of Fidesz. In the National Assembly, Kiss was a member of the National Cohesion Committee from 2014 to 2018, the Enterprise Development Committee from 2014 to 2015 and the Legislative Committee from 2015 to 2016.[1] He was one of the most active representatives of the National Assembly in the 2014–2018 parliamentary term, with more than 225 speeches and 579 motions. He was the first to propose tightening animal protection laws. He is primarily a supporter of several civil protection initiatives dealing with national policy, education policy and animal welfare.[2] He did not run in the 2018 parliamentary election, where he supported the joint candidate of MSZP and PM Tímea Szabó.
Kiss was nominated the joint mayoral candidate of MSZP, PM, Democratic Coalition (DK), Momentum Movement and Politics Can Be Different (LMP) in Óbuda (3rd district of Budapest) for the 2019 local elections. He defeated the long-time mayor Balázs Bús (Fidesz), becoming the first left-wing mayor of Óbuda since the transition to democracy. He was also elected to the municipal assembly as an individual representative.[3] Kiss switched from the Socialist Party to Democratic Coalition on 20 February 2020.[4] Following the DK going extra-parliamentary after the 2026 Hungarian parliamentary election, Kiss announced that he had left the party.[5]