Member of the National Assembly

The PUPS joined an electoral alliance led by the Socialist Party of Serbia for the 2008 parliamentary election. Čolaković was given the thirteenth position on the Socialist list and was chosen as part of the PUPS parliamentary delegation when the alliance won twenty mandates.^[8] (From 2000 to 2011, Serbian parliamentary mandates were awarded to sponsoring parties or coalitions rather than to individual candidates, and it was common practice for the mandates to be assigned out of numerical order. Čolaković did not automatically receive a mandate by virtue of his list position.)^[9][10] The results of the election were initially inconclusive, but the Socialists and their allies eventually formed a new coalition government with the For a European Serbia alliance. Čolaković led the PUPS assembly group in the parliament that followed.^[11]

Serbia's electoral system was reformed in 2011, such that parliamentary mandates were awarded in numerical order to candidates on successful lists. Čolaković was re-elected to the assembly in the elections of 2012 and 2014, in each case after receiving the eleventh position on the Socialist list (which won forty-four mandates each time).^[12] After the 2012 election, a new coalition government was formed by the Socialists, the Serbian Progressive Party, and other parties. The PUPS continued in government from 2012 to 2014 and provided parliamentary support to the government from 2014 to 2016.

The PUPS formed a new alliance with the Progressive Party for the 2016 Serbian parliamentary election. Čolaković received the seventy-fourth position on the Progressive list and was re-elected when it won a majority victory with 131 out of 250 mandates.^[13] During the 2016–20 assembly, he was member of the committee on finance, state budget, and control of public spending; a member of the committee on administrative, budgetary, mandate, and community issues; a deputy member of the European integration committee and the committee on the economy, regional development, trade, tourism, and energy; the head of Serbia's delegation to the Parliamentary Assembly of the Mediterranean; and a member of the parliamentary friendship groups with Azerbaijan, Belarus, Bosnia and Herzegovina, Croatia, Cuba, Kazakhstan, Montenegro, and Russia.^[14]

Čolaković stated in 2019 that he opposed the legal recognition of same-sex marriage. He also said that he was in favour of compulsory military service.^[15]

Member of the Assembly of Vojvodina

Čolaković did not seek re-election to the national assembly in 2020. He instead received the twenty-fourth position on the Progressive-led electoral list for the Vojvodina assembly in the that year's provincial election and was elected when the list won a majority victory with seventy-six out of 120 mandates.^[16] He is now a member of the provincial assembly's committee on economy and its committee on budget and finance.^[17]