At midnight, Ireland turned over the presidency of the EU to Lithuania.
At a celebration of Croatia's EU accession on Zagreb's main square, Gilmore said this "is a great moment for Croatia and for the European Union."
"We salute your efforts to meet the requirements for EU membership. We recognise the journey you have travelled. Your accession is a testament to the success of the European Union and you will be a beacon of hope for your neighbours in this part of Europe," he said shortly before midnight. "So, in a great Irish tradition, I bid the government and people of Croatia "cead mile faulte" - a hundred, thousand welcomes!"
Lithuanian President Dalia Grybauskaite was the first to congratulate Croatia after midnight. "Congratulations to Croatia! Congratulations to Europe! Finally, the Croatian people are with us!"
She said she was presenting Croatian President Ivo Josipovic with "a European team shirt" because "Croatia and Lithuania are basketball countries, so we know very well how important each and every team player is."
"From today on, Europe has yet another strong player. Let us score victories together," said Grybauskaite.