On 23 December 2011 the Croatian Parliament made a preliminary decision on EU accession and determined that the referendum would be held on 22 January 2012.

The Croatian State Election Committee was in charge of vote organization, ballot counting and result publication.

The outcome was welcomed by all political parties represented in Croatia's parliament; some right-wing politicians objected to the low turnout and what they consider a loss of independence.

[7] Voters traveling abroad were permitted to vote in the Croatian diplomatic missions as with Croatian presidential elections; however, the initial instructions by the Ministry of Public Administration did not allow voters within Croatia who were away from their place of residence to vote in the referendum, nor did it allow absentee ballots.

[15] The Election Committee announced that it would start publishing voting results on its web site two hours after the polling stations in Croatia closed, and it would expect to determine the referendum's outcome by midnight.

[24] Days after the 2011 parliamentary elections in early December 2011, it was suggested by Vesna Pusić – already recognized as the future Minister of Foreign and European Affairs – that the referendum should be postponed until March 2012 to allow better preparation for the poll.

[26] GONG's request was made because of what they stated to be: poor information provided to citizens; undefined procedures for voter registration away from a voter's permanent residence; unclear directions for voting abroad; no legal provisions specifically defining the composition of ballot counting commissions; no provisions for referendum vote monitoring by partisan, non-partisan and foreign monitors; no legal provisions regarding referendum funding (since the 2011 state budget did not appropriate any funds to cover referendum expenses); no legal provisions funding the pro-referendum campaign or allowing the campaign itself; and the lack of restrictions against campaigning on the day of the referendum.

The Labour party advocated postponing the referendum until 12 February in order to give more time to provide information on the consequences of EU membership.

[32] The referendum question was announced by the newly elected Prime Minister designate Zoran Milanović as "simple and bare":[33] "Are you for the membership of the Republic of Croatia in the European Union?

[36] The leading parliamentary political parties in Croatia have jointly supported EU accession since 2005, when a group called the Alliance for Europe (Croatian: Savez za Europu) was set up as an informal alliance aimed at achieving EU membership as a strategic goal of Croatian foreign policy.

The most substantial opposition to the accession came from the Croatian Party of Rights (HSP), which demanded that the government fund its television campaign against EU membership.

[41] During the 2011 parliamentary election campaign, HSP declared itself as the only party advocating rejection of Croatian EU accession;[42] it failed to win a single seat, receiving 3% of the votes.

[50] The Croatian Academy of Sciences and Arts also supported joining the EU with 93 academicians in favour, 2 against and 1 abstention; they said that the event represents a great opportunity for Croatia.

[53] Opinion polling regarding Croatian EU membership was regularly carried out by the CRO Demoskop, Ipsos Puls and Mediana Fides agencies.

[54] The lowest level of EU membership support (between 23% and 38%) was reported on 15–16 April 2011 in the wake of the ICTY's guilty verdict for Generals Gotovina and Markač.

Even though all Croatian citizens were voting in a single constituency for the referendum's purposes, the State Election Committee published the results by individual counties, cities, and municipalities.

[107] After the result's announcement, President Josipović commented that the day was of great significance to Croatia, defining the nation as one with a European future.

[108] The Croatian Minister of the Economy, Radimir Čačić, concluded that Croatia's credit rating would have been downgraded if the referendum had not passed.

Foreign and European Affairs Minister Vesna Pusić commented that the result was good news for Europe, which faced internal problems.

Former Speaker Vladimir Šeks said that the low turnout was caused by external factors – the debt crisis in Europe and a loss of confidence in Croatian political parties and institutions.

Sačić stated that the government had brought Croatia into a decaying organization in an illegitimate way, adding that the referendum result was a defeat of Croatian independence and they would challenge its validity in court.

[111] By the 3 March 2012 deadline, the Constitutional Court of Croatia received 22 appeals challenging the referendum's legality; it ruled against them all.

[112] Pursuant to the referendum's outcome, the Croatian parliament ratified the accession treaty unanimously (with 136 votes in favour) on 9 March 2012.