|Amid the eurozone's debt crisis, many Croatians say they are uncertain what EU membership will bring them [Reuters]
Croatia has signed an accession treaty to become the 28th member of the European Union in July 2013, following six years of negotiations with the regional bloc.
EU leaders in Brussels also decided on Friday to delay granting the country's fellow ex-Yugoslav neighbour, Serbia, the status of EU member candidate.
European Council president Herman Van Rompuy said: "The achievement of Croatia proves to all in the region that through hard work, persistence, political courage and determination, EU membership is within reach.
"Croatia is a pioneer, demonstrating in a tangible way that the future of the western Balkans as a whole lies in the European Union.
"The union committed to this perspective," Van Rompuy said at a signing ceremony remains on the sidelines of a summit of EU heads of state.
Croatia signed the deal as EU leaders, except Britain’s, came together to back tighter budget policing after a heated summit considered a last chance to save the debt-laden eurozone.
While many Croatians said they were uncertain what EU membership will bring them, they agreed there was no alternative to joining the bloc despite its current woes.
"Although I'm very concerned with developments within the European Union and the fact that the whole situation is unpredictable, we have no alternative," Nevenka Maric, a 36-year-old translator, told the AFP news agency.
The Adriatic state of 4.3m people accounts for less than one per cent of the EU's current population.
Its bid struggled due to concerns over corruption and Zagreb's slow progress in coming to terms with the legacy of Balkan wars in the 1990s.
A last-minute reform push, however, by outgoing Prime Minister Jadranka Kosor, persuaded the EU that Croatia was ready.
"This reform momentum now needs to be maintained," European Commission President Jose Manuel Barroso said.
Zagreb will face EU monitoring ahead of accession, with the EU executive expected to report on how well anti-corruption reforms are progressing.
Also at Friday’s summit, EU leaders decided that Serbia may have to wait until March to win the coveted status of membership candidate, which could be a prelude to launching entry talks with the EU.
In the meantime, Serbia will have to prove it is serious about improving relations with Kosovo.
Boris Tadic, Serbia’s president, expressed hope that his country would win EU status but also urged bloc leaders to show support and warned that further delays could give rise to anti-European sentiment.
"We didn't get it today, but I am certain we will get it another time," he said. "This decision is wind in the sails of those parties that don't want Serbia to join the European Union."