France has formally ratified the Lisbon Treaty, with its publication in the country's official journal.
The French lower house applauds after last week's vote
It is the fifth country to approve the reform treaty and the first of the EU's founder members to do so.
The French parliament voted to adopt the document last week, almost three years after a French No dealt a fatal blow to the European Constitution.
In a televised address, President Nicolas Sarkozy said "thanks to this success... France is back in Europe".
He had refused to put the treaty to a public vote, provoking the anger of opposition Socialist MPs.
Before it could be adopted by parliament, the upper and lower houses met in Congress at Versailles to delete a reference in the French constitution to the ill-fated EU Constitutional Treaty.
All 27 member states must approve the treaty before it can come into force as scheduled in 2009.
France joins Hungary, Malta, Slovenia and Romania as the countries to have ratified it so far. Ireland is the only EU member state due to hold a referendum.