Early years

Konstantinović joined the Democratic Party (Demokratska stranka, DS) in 1998.^[9] He briefly left the party in 2003, when Otpor! became a registered political party in its own right. Konstantinović appeared on Otpor!'s electoral list in the 2003 Serbian parliamentary election; the list failed to cross the electoral threshold to win representation in the assembly.^[10][11] After the election, he criticized Serbian prime minister Vojislav Koštunica's administration for including Milošević-era officials.^[12]

Otpor! merged into the Democratic Party in September 2004, and Konstantinović signed an accord with DS official Slobodan Gavrilović to formalize the merger.^[13] He was a member of the DS executive from 2004 to 2008.^[14]

Konstantinović appeared in the ninth position on the DS's list for the City Assembly of Belgrade in the 2004 local elections and was elected when list won thirty-four seats.^[15][16][17] He served for the next four years as a supporter of the city administration.^[18]

Parliamentarian

Konstantinović appeared in the 103rd position on the DS's electoral list in the 2007 parliamentary election.^[19] The list won sixty-four mandates, and he was included in the party's assembly delegation.^[20] (From 2000 to 2011, parliamentary mandates were awarded to sponsoring parties or coalitions rather than to individual candidates, and it was common practice for the mandates to be distributed out of numerical order. Konstantinović's position on the list – which was in any event mostly alphabetical – had no specific bearing on his chances of election.)^[21] After the election, the DS formed an unstable coalition government with the rival Democratic Party of Serbia (Demokratska stranka Srbije, DSS) and G17 Plus, and Konstantinović served as a supporter of the administration. In his first term, he was a member of the administrative committee and the committee for justice and state administration.^[22]

The DS–DSS alliance broke down in early 2008, and a new parliamentary election was called for May 2008. The DS contested the election at the head of the For a European Serbia (Za evropsku Srbiju, ZES) coalition. Konstantinović appeared in the eighty-ninth position on the list (which was again mostly arranged in alphabetical order) and was given a mandate when the list won a plurality victory with 102 out of 250 seats.^[23][24] The overall result of the election was inconclusive, but the ZES alliance ultimately formed a coalition government with the Socialist Party of Serbia (Socijalistička partija Srbije, SPS), and Konstantinović again supported the administration. He was a member of the committee for justice and state administration and the committee for urban planning and construction; a deputy member of the committee on constitutional affairs, the committee on foreign affairs, and the committee for European integration; and a member of the parliamentary friendship group with the United States of America.^[25] In January 2009, he replaced Tomislav Nikolić as chair of the administrative committee.^[26] In this capacity, he initiated the launch of an "e-parliament" for the assembly. In the same period, he led a working group reviewing the assembly's code of conduct.^[27]

Serbia's electoral system was reformed in 2011, such that parliamentary mandates were awarded in numerical order to candidates on successful lists. Konstantinović was given the sixty-fourth position on the Democratic Party's Choice for a Better Life coalition list in the 2012 election and was narrowly re-elected when the list won sixty-seventh mandates.^[28] The Serbian Progressive Party (Srpska napredna stranka, SNS) formed a new coalition government with the SPS and other parties after the election, and the DS moved into opposition. During his third term, Konstantinović was a member of the committee for justice, state administration, and local self-government; a deputy member of the security services control board and the committee on administrative, budgetary, mandate, and immunity issues; a deputy member of Serbia's delegation to the OSCE parliamentary assembly; and a member of the friendship groups with Croatia, Germany, Slovakia, the United Kingdom, and the United States.^[29]

Konstantinović did not seek re-election to the Belgrade city assembly in the 2008 local elections but instead appeared on the ZES list for the municipal assembly of Savski Venac, one of Belgrade's seventeen constituent municipalities.^[30] He received a mandate when the list won a plurality victory with seventeen out of twenty-seven seats.^[31][32] He was later given the eleventh position on the DS's list in the 2012 local elections and was re-elected when the list won sixteen seats.^[33][34]