The building was nearly completely destroyed in the 1991 military aggression.
Addressing the ceremony, President Josipovic voiced confidence that Vukovar, despite what it had gone through in recent history, could become a champion of reconciliation and coexistence. "It is much harder to build than destroy and therein lies our biggest responsibility. I believe we can heal the wounds and move on together."
Recalling that the European Union was built on the "never again" motto, he said today's generations of Croats had the strength and power to make that motto happen, while the strength of future generations to do so would depend on "whether we have this strength today."
Martinez said the EU would help in the interior restoration of the Workers Hall and that it would be scandalous if only the front was renovated.
Europe has been for centuries the scene of war destruction such as the one Vukovar suffered in the 1991-95 Homeland War, he said.
It is not only that hundreds or thousands of people were massacred, but millions of people were killed through the centuries as a consequence of war and crazy violence, Martinez said, pushing for a Europe of unity and progress.
Speaking on behalf of the premier, War Veterans Minister Predrag Matic asked the representatives of the international community to understand everything that happened and was happening in Vukovar.
"Fifteen years have passed since the peaceful reintegration and it all looks nice from outside, but much more is necessary to restore order in the souls of Vukovar's residents... The government's efforts won't be enough without your support and understanding of everything that happened in Vukovar."
The head of the EU Delegation to Croatia, Paul Vandoren, said the Workers Hall was a symbol of Vukovar's rich history as well as of the horrible war destruction, adding that this building was reborn today to become a symbol of Vukovar's new future.
Speeches were also delivered by the permanent representative of the UN Development Programme to Croatia, Louisa Vinton, and local officials.
The building of the Workers Hall was built in 1897 as the Grand Hotel and before the Homeland War it was best known as the location of the Yugoslav Communist Party's second congress.
About EUR 2.7 million has to be secured to renovate the building's interior, while EUR 1.64 million was invested in the renovation of the front by the European Parliament and the Croatian Regional Development and EU Funds Ministry. The incentive to reconstruct the building came from the European Parliament which launched a regional initiative of post-war reconstruction and reconciliation through the restoration of monuments destroyed in the Homeland War.
At today's ceremony, Vukovar Mayor Zeljko Sabo presented Martinez, Vandoren and Vinton with thanksgiving charters. Before the ceremony, Martinez and Leko took part in a public discussion on the upcoming Croatian election for members of the European Parliament.