Czech president Vaclav Klaus, who is widely known as a Eurosceptic, has put his pen to the EU’s Lisbon Treaty agreement.
The document paves the way for the streamlining of the Union's decision making process.
This removes the last hurdle to a united Europe and comes just hours after a court rejected a complaint about the agreement.
The Lisbon Treaty has now been approved by all 27 member states and it is hoped will transform Europe into a more influential global player.
The end of the ratification is expected to speed up the signing of a new strategic partnership between Russia and the EU.